diff options
Diffstat (limited to 'Documentation/PCI')
| -rw-r--r-- | Documentation/PCI/00-INDEX | 14 | ||||
| -rw-r--r-- | Documentation/PCI/MSI-HOWTO.txt | 359 | ||||
| -rw-r--r-- | Documentation/PCI/PCI-DMA-mapping.txt | 766 | ||||
| -rw-r--r-- | Documentation/PCI/PCIEBUS-HOWTO.txt | 217 | ||||
| -rw-r--r-- | Documentation/PCI/pci-error-recovery.txt | 431 | ||||
| -rw-r--r-- | Documentation/PCI/pci-iov-howto.txt | 99 | ||||
| -rw-r--r-- | Documentation/PCI/pci.txt | 651 | ||||
| -rw-r--r-- | Documentation/PCI/pcieaer-howto.txt | 273 |
8 files changed, 2810 insertions, 0 deletions
diff --git a/Documentation/PCI/00-INDEX b/Documentation/PCI/00-INDEX new file mode 100644 index 00000000000..812b17fe3ed --- /dev/null +++ b/Documentation/PCI/00-INDEX @@ -0,0 +1,14 @@ +00-INDEX + - this file +MSI-HOWTO.txt + - the Message Signaled Interrupts (MSI) Driver Guide HOWTO and FAQ. +PCI-DMA-mapping.txt + - info for PCI drivers using DMA portably across all platforms +PCIEBUS-HOWTO.txt + - a guide describing the PCI Express Port Bus driver +pci-error-recovery.txt + - info on PCI error recovery +pci.txt + - info on the PCI subsystem for device driver authors +pcieaer-howto.txt + - the PCI Express Advanced Error Reporting Driver Guide HOWTO diff --git a/Documentation/PCI/MSI-HOWTO.txt b/Documentation/PCI/MSI-HOWTO.txt new file mode 100644 index 00000000000..dcf7acc720e --- /dev/null +++ b/Documentation/PCI/MSI-HOWTO.txt @@ -0,0 +1,359 @@ + The MSI Driver Guide HOWTO + Tom L Nguyen tom.l.nguyen@intel.com + 10/03/2003 + Revised Feb 12, 2004 by Martine Silbermann + email: Martine.Silbermann@hp.com + Revised Jun 25, 2004 by Tom L Nguyen + Revised Jul 9, 2008 by Matthew Wilcox <willy@linux.intel.com> + Copyright 2003, 2008 Intel Corporation + +1. About this guide + +This guide describes the basics of Message Signaled Interrupts (MSIs), +the advantages of using MSI over traditional interrupt mechanisms, how +to change your driver to use MSI or MSI-X and some basic diagnostics to +try if a device doesn't support MSIs. + + +2. What are MSIs? + +A Message Signaled Interrupt is a write from the device to a special +address which causes an interrupt to be received by the CPU. + +The MSI capability was first specified in PCI 2.2 and was later enhanced +in PCI 3.0 to allow each interrupt to be masked individually. The MSI-X +capability was also introduced with PCI 3.0. It supports more interrupts +per device than MSI and allows interrupts to be independently configured. + +Devices may support both MSI and MSI-X, but only one can be enabled at +a time. + + +3. Why use MSIs? + +There are three reasons why using MSIs can give an advantage over +traditional pin-based interrupts. + +Pin-based PCI interrupts are often shared amongst several devices. +To support this, the kernel must call each interrupt handler associated +with an interrupt, which leads to reduced performance for the system as +a whole. MSIs are never shared, so this problem cannot arise. + +When a device writes data to memory, then raises a pin-based interrupt, +it is possible that the interrupt may arrive before all the data has +arrived in memory (this becomes more likely with devices behind PCI-PCI +bridges). In order to ensure that all the data has arrived in memory, +the interrupt handler must read a register on the device which raised +the interrupt. PCI transaction ordering rules require that all the data +arrives in memory before the value can be returned from the register. +Using MSIs avoids this problem as the interrupt-generating write cannot +pass the data writes, so by the time the interrupt is raised, the driver +knows that all the data has arrived in memory. + +PCI devices can only support a single pin-based interrupt per function. +Often drivers have to query the device to find out what event has +occurred, slowing down interrupt handling for the common case. With +MSIs, a device can support more interrupts, allowing each interrupt +to be specialised to a different purpose. One possible design gives +infrequent conditions (such as errors) their own interrupt which allows +the driver to handle the normal interrupt handling path more efficiently. +Other possible designs include giving one interrupt to each packet queue +in a network card or each port in a storage controller. + + +4. How to use MSIs + +PCI devices are initialised to use pin-based interrupts. The device +driver has to set up the device to use MSI or MSI-X. Not all machines +support MSIs correctly, and for those machines, the APIs described below +will simply fail and the device will continue to use pin-based interrupts. + +4.1 Include kernel support for MSIs + +To support MSI or MSI-X, the kernel must be built with the CONFIG_PCI_MSI +option enabled. This option is only available on some architectures, +and it may depend on some other options also being set. For example, +on x86, you must also enable X86_UP_APIC or SMP in order to see the +CONFIG_PCI_MSI option. + +4.2 Using MSI + +Most of the hard work is done for the driver in the PCI layer. It simply +has to request that the PCI layer set up the MSI capability for this +device. + +4.2.1 pci_enable_msi + +int pci_enable_msi(struct pci_dev *dev) + +A successful call will allocate ONE interrupt to the device, regardless +of how many MSIs the device supports. The device will be switched from +pin-based interrupt mode to MSI mode. The dev->irq number is changed +to a new number which represents the message signaled interrupt. +This function should be called before the driver calls request_irq() +since enabling MSIs disables the pin-based IRQ and the driver will not +receive interrupts on the old interrupt. + +4.2.2 pci_enable_msi_block + +int pci_enable_msi_block(struct pci_dev *dev, int count) + +This variation on the above call allows a device driver to request multiple +MSIs. The MSI specification only allows interrupts to be allocated in +powers of two, up to a maximum of 2^5 (32). + +If this function returns 0, it has succeeded in allocating at least as many +interrupts as the driver requested (it may have allocated more in order +to satisfy the power-of-two requirement). In this case, the function +enables MSI on this device and updates dev->irq to be the lowest of +the new interrupts assigned to it. The other interrupts assigned to +the device are in the range dev->irq to dev->irq + count - 1. + +If this function returns a negative number, it indicates an error and +the driver should not attempt to request any more MSI interrupts for +this device. If this function returns a positive number, it will be +less than 'count' and indicate the number of interrupts that could have +been allocated. In neither case will the irq value have been +updated, nor will the device have been switched into MSI mode. + +The device driver must decide what action to take if +pci_enable_msi_block() returns a value less than the number asked for. +Some devices can make use of fewer interrupts than the maximum they +request; in this case the driver should call pci_enable_msi_block() +again. Note that it is not guaranteed to succeed, even when the +'count' has been reduced to the value returned from a previous call to +pci_enable_msi_block(). This is because there are multiple constraints +on the number of vectors that can be allocated; pci_enable_msi_block() +will return as soon as it finds any constraint that doesn't allow the +call to succeed. + +4.2.3 pci_disable_msi + +void pci_disable_msi(struct pci_dev *dev) + +This function should be used to undo the effect of pci_enable_msi() or +pci_enable_msi_block(). Calling it restores dev->irq to the pin-based +interrupt number and frees the previously allocated message signaled +interrupt(s). The interrupt may subsequently be assigned to another +device, so drivers should not cache the value of dev->irq. + +A device driver must always call free_irq() on the interrupt(s) +for which it has called request_irq() before calling this function. +Failure to do so will result in a BUG_ON(), the device will be left with +MSI enabled and will leak its vector. + +4.3 Using MSI-X + +The MSI-X capability is much more flexible than the MSI capability. +It supports up to 2048 interrupts, each of which can be controlled +independently. To support this flexibility, drivers must use an array of +`struct msix_entry': + +struct msix_entry { + u16 vector; /* kernel uses to write alloc vector */ + u16 entry; /* driver uses to specify entry */ +}; + +This allows for the device to use these interrupts in a sparse fashion; +for example it could use interrupts 3 and 1027 and allocate only a +two-element array. The driver is expected to fill in the 'entry' value +in each element of the array to indicate which entries it wants the kernel +to assign interrupts for. It is invalid to fill in two entries with the +same number. + +4.3.1 pci_enable_msix + +int pci_enable_msix(struct pci_dev *dev, struct msix_entry *entries, int nvec) + +Calling this function asks the PCI subsystem to allocate 'nvec' MSIs. +The 'entries' argument is a pointer to an array of msix_entry structs +which should be at least 'nvec' entries in size. On success, the +function will return 0 and the device will have been switched into +MSI-X interrupt mode. The 'vector' elements in each entry will have +been filled in with the interrupt number. The driver should then call +request_irq() for each 'vector' that it decides to use. + +If this function returns a negative number, it indicates an error and +the driver should not attempt to allocate any more MSI-X interrupts for +this device. If it returns a positive number, it indicates the maximum +number of interrupt vectors that could have been allocated. See example +below. + +This function, in contrast with pci_enable_msi(), does not adjust +dev->irq. The device will not generate interrupts for this interrupt +number once MSI-X is enabled. The device driver is responsible for +keeping track of the interrupts assigned to the MSI-X vectors so it can +free them again later. + +Device drivers should normally call this function once per device +during the initialization phase. + +It is ideal if drivers can cope with a variable number of MSI-X interrupts, +there are many reasons why the platform may not be able to provide the +exact number a driver asks for. + +A request loop to achieve that might look like: + +static int foo_driver_enable_msix(struct foo_adapter *adapter, int nvec) +{ + while (nvec >= FOO_DRIVER_MINIMUM_NVEC) { + rc = pci_enable_msix(adapter->pdev, + adapter->msix_entries, nvec); + if (rc > 0) + nvec = rc; + else + return rc; + } + + return -ENOSPC; +} + +4.3.2 pci_disable_msix + +void pci_disable_msix(struct pci_dev *dev) + +This API should be used to undo the effect of pci_enable_msix(). It frees +the previously allocated message signaled interrupts. The interrupts may +subsequently be assigned to another device, so drivers should not cache +the value of the 'vector' elements over a call to pci_disable_msix(). + +A device driver must always call free_irq() on the interrupt(s) +for which it has called request_irq() before calling this function. +Failure to do so will result in a BUG_ON(), the device will be left with +MSI enabled and will leak its vector. + +4.3.3 The MSI-X Table + +The MSI-X capability specifies a BAR and offset within that BAR for the +MSI-X Table. This address is mapped by the PCI subsystem, and should not +be accessed directly by the device driver. If the driver wishes to +mask or unmask an interrupt, it should call disable_irq() / enable_irq(). + +4.4 Handling devices implementing both MSI and MSI-X capabilities + +If a device implements both MSI and MSI-X capabilities, it can +run in either MSI mode or MSI-X mode but not both simultaneously. +This is a requirement of the PCI spec, and it is enforced by the +PCI layer. Calling pci_enable_msi() when MSI-X is already enabled or +pci_enable_msix() when MSI is already enabled will result in an error. +If a device driver wishes to switch between MSI and MSI-X at runtime, +it must first quiesce the device, then switch it back to pin-interrupt +mode, before calling pci_enable_msi() or pci_enable_msix() and resuming +operation. This is not expected to be a common operation but may be +useful for debugging or testing during development. + +4.5 Considerations when using MSIs + +4.5.1 Choosing between MSI-X and MSI + +If your device supports both MSI-X and MSI capabilities, you should use +the MSI-X facilities in preference to the MSI facilities. As mentioned +above, MSI-X supports any number of interrupts between 1 and 2048. +In constrast, MSI is restricted to a maximum of 32 interrupts (and +must be a power of two). In addition, the MSI interrupt vectors must +be allocated consecutively, so the system may not be able to allocate +as many vectors for MSI as it could for MSI-X. On some platforms, MSI +interrupts must all be targetted at the same set of CPUs whereas MSI-X +interrupts can all be targetted at different CPUs. + +4.5.2 Spinlocks + +Most device drivers have a per-device spinlock which is taken in the +interrupt handler. With pin-based interrupts or a single MSI, it is not +necessary to disable interrupts (Linux guarantees the same interrupt will +not be re-entered). If a device uses multiple interrupts, the driver +must disable interrupts while the lock is held. If the device sends +a different interrupt, the driver will deadlock trying to recursively +acquire the spinlock. + +There are two solutions. The first is to take the lock with +spin_lock_irqsave() or spin_lock_irq() (see +Documentation/DocBook/kernel-locking). The second is to specify +IRQF_DISABLED to request_irq() so that the kernel runs the entire +interrupt routine with interrupts disabled. + +If your MSI interrupt routine does not hold the lock for the whole time +it is running, the first solution may be best. The second solution is +normally preferred as it avoids making two transitions from interrupt +disabled to enabled and back again. + +4.6 How to tell whether MSI/MSI-X is enabled on a device + +Using 'lspci -v' (as root) may show some devices with "MSI", "Message +Signalled Interrupts" or "MSI-X" capabilities. Each of these capabilities +has an 'Enable' flag which will be followed with either "+" (enabled) +or "-" (disabled). + + +5. MSI quirks + +Several PCI chipsets or devices are known not to support MSIs. +The PCI stack provides three ways to disable MSIs: + +1. globally +2. on all devices behind a specific bridge +3. on a single device + +5.1. Disabling MSIs globally + +Some host chipsets simply don't support MSIs properly. If we're +lucky, the manufacturer knows this and has indicated it in the ACPI +FADT table. In this case, Linux will automatically disable MSIs. +Some boards don't include this information in the table and so we have +to detect them ourselves. The complete list of these is found near the +quirk_disable_all_msi() function in drivers/pci/quirks.c. + +If you have a board which has problems with MSIs, you can pass pci=nomsi +on the kernel command line to disable MSIs on all devices. It would be +in your best interests to report the problem to linux-pci@vger.kernel.org +including a full 'lspci -v' so we can add the quirks to the kernel. + +5.2. Disabling MSIs below a bridge + +Some PCI bridges are not able to route MSIs between busses properly. +In this case, MSIs must be disabled on all devices behind the bridge. + +Some bridges allow you to enable MSIs by changing some bits in their +PCI configuration space (especially the Hypertransport chipsets such +as the nVidia nForce and Serverworks HT2000). As with host chipsets, +Linux mostly knows about them and automatically enables MSIs if it can. +If you have a bridge which Linux doesn't yet know about, you can enable +MSIs in configuration space using whatever method you know works, then +enable MSIs on that bridge by doing: + + echo 1 > /sys/bus/pci/devices/$bridge/msi_bus + +where $bridge is the PCI address of the bridge you've enabled (eg +0000:00:0e.0). + +To disable MSIs, echo 0 instead of 1. Changing this value should be +done with caution as it can break interrupt handling for all devices +below this bridge. + +Again, please notify linux-pci@vger.kernel.org of any bridges that need +special handling. + +5.3. Disabling MSIs on a single device + +Some devices are known to have faulty MSI implementations. Usually this +is handled in the individual device driver but occasionally it's necessary +to handle this with a quirk. Some drivers have an option to disable use +of MSI. While this is a convenient workaround for the driver author, +it is not good practise, and should not be emulated. + +5.4. Finding why MSIs are disabled on a device + +From the above three sections, you can see that there are many reasons +why MSIs may not be enabled for a given device. Your first step should +be to examine your dmesg carefully to determine whether MSIs are enabled +for your machine. You should also check your .config to be sure you +have enabled CONFIG_PCI_MSI. + +Then, 'lspci -t' gives the list of bridges above a device. Reading +/sys/bus/pci/devices/*/msi_bus will tell you whether MSI are enabled (1) +or disabled (0). If 0 is found in any of the msi_bus files belonging +to bridges between the PCI root and the device, MSIs are disabled. + +It is also worth checking the device driver to see whether it supports MSIs. +For example, it may contain calls to pci_enable_msi(), pci_enable_msix() or +pci_enable_msi_block(). diff --git a/Documentation/PCI/PCI-DMA-mapping.txt b/Documentation/PCI/PCI-DMA-mapping.txt new file mode 100644 index 00000000000..ecad88d9fe5 --- /dev/null +++ b/Documentation/PCI/PCI-DMA-mapping.txt @@ -0,0 +1,766 @@ + Dynamic DMA mapping + =================== + + David S. Miller <davem@redhat.com> + Richard Henderson <rth@cygnus.com> + Jakub Jelinek <jakub@redhat.com> + +This document describes the DMA mapping system in terms of the pci_ +API. For a similar API that works for generic devices, see +DMA-API.txt. + +Most of the 64bit platforms have special hardware that translates bus +addresses (DMA addresses) into physical addresses. This is similar to +how page tables and/or a TLB translates virtual addresses to physical +addresses on a CPU. This is needed so that e.g. PCI devices can +access with a Single Address Cycle (32bit DMA address) any page in the +64bit physical address space. Previously in Linux those 64bit +platforms had to set artificial limits on the maximum RAM size in the +system, so that the virt_to_bus() static scheme works (the DMA address +translation tables were simply filled on bootup to map each bus +address to the physical page __pa(bus_to_virt())). + +So that Linux can use the dynamic DMA mapping, it needs some help from the +drivers, namely it has to take into account that DMA addresses should be +mapped only for the time they are actually used and unmapped after the DMA +transfer. + +The following API will work of course even on platforms where no such +hardware exists, see e.g. arch/x86/include/asm/pci.h for how it is implemented on +top of the virt_to_bus interface. + +First of all, you should make sure + +#include <linux/pci.h> + +is in your driver. This file will obtain for you the definition of the +dma_addr_t (which can hold any valid DMA address for the platform) +type which should be used everywhere you hold a DMA (bus) address +returned from the DMA mapping functions. + + What memory is DMA'able? + +The first piece of information you must know is what kernel memory can +be used with the DMA mapping facilities. There has been an unwritten +set of rules regarding this, and this text is an attempt to finally +write them down. + +If you acquired your memory via the page allocator +(i.e. __get_free_page*()) or the generic memory allocators +(i.e. kmalloc() or kmem_cache_alloc()) then you may DMA to/from +that memory using the addresses returned from those routines. + +This means specifically that you may _not_ use the memory/addresses +returned from vmalloc() for DMA. It is possible to DMA to the +_underlying_ memory mapped into a vmalloc() area, but this requires +walking page tables to get the physical addresses, and then +translating each of those pages back to a kernel address using +something like __va(). [ EDIT: Update this when we integrate +Gerd Knorr's generic code which does this. ] + +This rule also means that you may use neither kernel image addresses +(items in data/text/bss segments), nor module image addresses, nor +stack addresses for DMA. These could all be mapped somewhere entirely +different than the rest of physical memory. Even if those classes of +memory could physically work with DMA, you'd need to ensure the I/O +buffers were cacheline-aligned. Without that, you'd see cacheline +sharing problems (data corruption) on CPUs with DMA-incoherent caches. +(The CPU could write to one word, DMA would write to a different one +in the same cache line, and one of them could be overwritten.) + +Also, this means that you cannot take the return of a kmap() +call and DMA to/from that. This is similar to vmalloc(). + +What about block I/O and networking buffers? The block I/O and +networking subsystems make sure that the buffers they use are valid +for you to DMA from/to. + + DMA addressing limitations + +Does your device have any DMA addressing limitations? For example, is +your device only capable of driving the low order 24-bits of address +on the PCI bus for SAC DMA transfers? If so, you need to inform the +PCI layer of this fact. + +By default, the kernel assumes that your device can address the full +32-bits in a SAC cycle. For a 64-bit DAC capable device, this needs +to be increased. And for a device with limitations, as discussed in +the previous paragraph, it needs to be decreased. + +pci_alloc_consistent() by default will return 32-bit DMA addresses. +PCI-X specification requires PCI-X devices to support 64-bit +addressing (DAC) for all transactions. And at least one platform (SGI +SN2) requires 64-bit consistent allocations to operate correctly when +the IO bus is in PCI-X mode. Therefore, like with pci_set_dma_mask(), +it's good practice to call pci_set_consistent_dma_mask() to set the +appropriate mask even if your device only supports 32-bit DMA +(default) and especially if it's a PCI-X device. + +For correct operation, you must interrogate the PCI layer in your +device probe routine to see if the PCI controller on the machine can +properly support the DMA addressing limitation your device has. It is +good style to do this even if your device holds the default setting, +because this shows that you did think about these issues wrt. your +device. + +The query is performed via a call to pci_set_dma_mask(): + + int pci_set_dma_mask(struct pci_dev *pdev, u64 device_mask); + +The query for consistent allocations is performed via a call to +pci_set_consistent_dma_mask(): + + int pci_set_consistent_dma_mask(struct pci_dev *pdev, u64 device_mask); + +Here, pdev is a pointer to the PCI device struct of your device, and +device_mask is a bit mask describing which bits of a PCI address your +device supports. It returns zero if your card can perform DMA +properly on the machine given the address mask you provided. + +If it returns non-zero, your device cannot perform DMA properly on +this platform, and attempting to do so will result in undefined +behavior. You must either use a different mask, or not use DMA. + +This means that in the failure case, you have three options: + +1) Use another DMA mask, if possible (see below). +2) Use some non-DMA mode for data transfer, if possible. +3) Ignore this device and do not initialize it. + +It is recommended that your driver print a kernel KERN_WARNING message +when you end up performing either #2 or #3. In this manner, if a user +of your driver reports that performance is bad or that the device is not +even detected, you can ask them for the kernel messages to find out +exactly why. + +The standard 32-bit addressing PCI device would do something like +this: + + if (pci_set_dma_mask(pdev, DMA_BIT_MASK(32))) { + printk(KERN_WARNING + "mydev: No suitable DMA available.\n"); + goto ignore_this_device; + } + +Another common scenario is a 64-bit capable device. The approach +here is to try for 64-bit DAC addressing, but back down to a +32-bit mask should that fail. The PCI platform code may fail the +64-bit mask not because the platform is not capable of 64-bit +addressing. Rather, it may fail in this case simply because +32-bit SAC addressing is done more efficiently than DAC addressing. +Sparc64 is one platform which behaves in this way. + +Here is how you would handle a 64-bit capable device which can drive +all 64-bits when accessing streaming DMA: + + int using_dac; + + if (!pci_set_dma_mask(pdev, DMA_BIT_MASK(64))) { + using_dac = 1; + } else if (!pci_set_dma_mask(pdev, DMA_BIT_MASK(32))) { + using_dac = 0; + } else { + printk(KERN_WARNING + "mydev: No suitable DMA available.\n"); + goto ignore_this_device; + } + +If a card is capable of using 64-bit consistent allocations as well, +the case would look like this: + + int using_dac, consistent_using_dac; + + if (!pci_set_dma_mask(pdev, DMA_BIT_MASK(64))) { + using_dac = 1; + consistent_using_dac = 1; + pci_set_consistent_dma_mask(pdev, DMA_BIT_MASK(64)); + } else if (!pci_set_dma_mask(pdev, DMA_BIT_MASK(32))) { + using_dac = 0; + consistent_using_dac = 0; + pci_set_consistent_dma_mask(pdev, DMA_BIT_MASK(32)); + } else { + printk(KERN_WARNING + "mydev: No suitable DMA available.\n"); + goto ignore_this_device; + } + +pci_set_consistent_dma_mask() will always be able to set the same or a +smaller mask as pci_set_dma_mask(). However for the rare case that a +device driver only uses consistent allocations, one would have to +check the return value from pci_set_consistent_dma_mask(). + +Finally, if your device can only drive the low 24-bits of +address during PCI bus mastering you might do something like: + + if (pci_set_dma_mask(pdev, DMA_BIT_MASK(24))) { + printk(KERN_WARNING + "mydev: 24-bit DMA addressing not available.\n"); + goto ignore_this_device; + } + +When pci_set_dma_mask() is successful, and returns zero, the PCI layer +saves away this mask you have provided. The PCI layer will use this +information later when you make DMA mappings. + +There is a case which we are aware of at this time, which is worth +mentioning in this documentation. If your device supports multiple +functions (for example a sound card provides playback and record +functions) and the various different functions have _different_ +DMA addressing limitations, you may wish to probe each mask and +only provide the functionality which the machine can handle. It +is important that the last call to pci_set_dma_mask() be for the +most specific mask. + +Here is pseudo-code showing how this might be done: + + #define PLAYBACK_ADDRESS_BITS DMA_BIT_MASK(32) + #define RECORD_ADDRESS_BITS DMA_BIT_MASK(24) + + struct my_sound_card *card; + struct pci_dev *pdev; + + ... + if (!pci_set_dma_mask(pdev, PLAYBACK_ADDRESS_BITS)) { + card->playback_enabled = 1; + } else { + card->playback_enabled = 0; + printk(KERN_WARNING "%s: Playback disabled due to DMA limitations.\n", + card->name); + } + if (!pci_set_dma_mask(pdev, RECORD_ADDRESS_BITS)) { + card->record_enabled = 1; + } else { + card->record_enabled = 0; + printk(KERN_WARNING "%s: Record disabled due to DMA limitations.\n", + card->name); + } + +A sound card was used as an example here because this genre of PCI +devices seems to be littered with ISA chips given a PCI front end, +and thus retaining the 16MB DMA addressing limitations of ISA. + + Types of DMA mappings + +There are two types of DMA mappings: + +- Consistent DMA mappings which are usually mapped at driver + initialization, unmapped at the end and for which the hardware should + guarantee that the device and the CPU can access the data + in parallel and will see updates made by each other without any + explicit software flushing. + + Think of "consistent" as "synchronous" or "coherent". + + The current default is to return consistent memory in the low 32 + bits of the PCI bus space. However, for future compatibility you + should set the consistent mask even if this default is fine for your + driver. + + Good examples of what to use consistent mappings for are: + + - Network card DMA ring descriptors. + - SCSI adapter mailbox command data structures. + - Device firmware microcode executed out of + main memory. + + The invariant these examples all require is that any CPU store + to memory is immediately visible to the device, and vice + versa. Consistent mappings guarantee this. + + IMPORTANT: Consistent DMA memory does not preclude the usage of + proper memory barriers. The CPU may reorder stores to + consistent memory just as it may normal memory. Example: + if it is important for the device to see the first word + of a descriptor updated before the second, you must do + something like: + + desc->word0 = address; + wmb(); + desc->word1 = DESC_VALID; + + in order to get correct behavior on all platforms. + + Also, on some platforms your driver may need to flush CPU write + buffers in much the same way as it needs to flush write buffers + found in PCI bridges (such as by reading a register's value + after writing it). + +- Streaming DMA mappings which are usually mapped for one DMA transfer, + unmapped right after it (unless you use pci_dma_sync_* below) and for which + hardware can optimize for sequential accesses. + + This of "streaming" as "asynchronous" or "outside the coherency + domain". + + Good examples of what to use streaming mappings for are: + + - Networking buffers transmitted/received by a device. + - Filesystem buffers written/read by a SCSI device. + + The interfaces for using this type of mapping were designed in + such a way that an implementation can make whatever performance + optimizations the hardware allows. To this end, when using + such mappings you must be explicit about what you want to happen. + +Neither type of DMA mapping has alignment restrictions that come +from PCI, although some devices may have such restrictions. +Also, systems with caches that aren't DMA-coherent will work better +when the underlying buffers don't share cache lines with other data. + + + Using Consistent DMA mappings. + +To allocate and map large (PAGE_SIZE or so) consistent DMA regions, +you should do: + + dma_addr_t dma_handle; + + cpu_addr = pci_alloc_consistent(pdev, size, &dma_handle); + +where pdev is a struct pci_dev *. This may be called in interrupt context. +You should use dma_alloc_coherent (see DMA-API.txt) for buses +where devices don't have struct pci_dev (like ISA, EISA). + +This argument is needed because the DMA translations may be bus +specific (and often is private to the bus which the device is attached +to). + +Size is the length of the region you want to allocate, in bytes. + +This routine will allocate RAM for that region, so it acts similarly to +__get_free_pages (but takes size instead of a page order). If your +driver needs regions sized smaller than a page, you may prefer using +the pci_pool interface, described below. + +The consistent DMA mapping interfaces, for non-NULL pdev, will by +default return a DMA address which is SAC (Single Address Cycle) +addressable. Even if the device indicates (via PCI dma mask) that it +may address the upper 32-bits and thus perform DAC cycles, consistent +allocation will only return > 32-bit PCI addresses for DMA if the +consistent dma mask has been explicitly changed via +pci_set_consistent_dma_mask(). This is true of the pci_pool interface +as well. + +pci_alloc_consistent returns two values: the virtual address which you +can use to access it from the CPU and dma_handle which you pass to the +card. + +The cpu return address and the DMA bus master address are both +guaranteed to be aligned to the smallest PAGE_SIZE order which +is greater than or equal to the requested size. This invariant +exists (for example) to guarantee that if you allocate a chunk +which is smaller than or equal to 64 kilobytes, the extent of the +buffer you receive will not cross a 64K boundary. + +To unmap and free such a DMA region, you call: + + pci_free_consistent(pdev, size, cpu_addr, dma_handle); + +where pdev, size are the same as in the above call and cpu_addr and +dma_handle are the values pci_alloc_consistent returned to you. +This function may not be called in interrupt context. + +If your driver needs lots of smaller memory regions, you can write +custom code to subdivide pages returned by pci_alloc_consistent, +or you can use the pci_pool API to do that. A pci_pool is like +a kmem_cache, but it uses pci_alloc_consistent not __get_free_pages. +Also, it understands common hardware constraints for alignment, +like queue heads needing to be aligned on N byte boundaries. + +Create a pci_pool like this: + + struct pci_pool *pool; + + pool = pci_pool_create(name, pdev, size, align, alloc); + +The "name" is for diagnostics (like a kmem_cache name); pdev and size +are as above. The device's hardware alignment requirement for this +type of data is "align" (which is expressed in bytes, and must be a +power of two). If your device has no boundary crossing restrictions, +pass 0 for alloc; passing 4096 says memory allocated from this pool +must not cross 4KByte boundaries (but at that time it may be better to +go for pci_alloc_consistent directly instead). + +Allocate memory from a pci pool like this: + + cpu_addr = pci_pool_alloc(pool, flags, &dma_handle); + +flags are SLAB_KERNEL if blocking is permitted (not in_interrupt nor +holding SMP locks), SLAB_ATOMIC otherwise. Like pci_alloc_consistent, +this returns two values, cpu_addr and dma_handle. + +Free memory that was allocated from a pci_pool like this: + + pci_pool_free(pool, cpu_addr, dma_handle); + +where pool is what you passed to pci_pool_alloc, and cpu_addr and +dma_handle are the values pci_pool_alloc returned. This function +may be called in interrupt context. + +Destroy a pci_pool by calling: + + pci_pool_destroy(pool); + +Make sure you've called pci_pool_free for all memory allocated +from a pool before you destroy the pool. This function may not +be called in interrupt context. + + DMA Direction + +The interfaces described in subsequent portions of this document +take a DMA direction argument, which is an integer and takes on +one of the following values: + + PCI_DMA_BIDIRECTIONAL + PCI_DMA_TODEVICE + PCI_DMA_FROMDEVICE + PCI_DMA_NONE + +One should provide the exact DMA direction if you know it. + +PCI_DMA_TODEVICE means "from main memory to the PCI device" +PCI_DMA_FROMDEVICE means "from the PCI device to main memory" +It is the direction in which the data moves during the DMA +transfer. + +You are _strongly_ encouraged to specify this as precisely +as you possibly can. + +If you absolutely cannot know the direction of the DMA transfer, +specify PCI_DMA_BIDIRECTIONAL. It means that the DMA can go in +either direction. The platform guarantees that you may legally +specify this, and that it will work, but this may be at the +cost of performance for example. + +The value PCI_DMA_NONE is to be used for debugging. One can +hold this in a data structure before you come to know the +precise direction, and this will help catch cases where your +direction tracking logic has failed to set things up properly. + +Another advantage of specifying this value precisely (outside of +potential platform-specific optimizations of such) is for debugging. +Some platforms actually have a write permission boolean which DMA +mappings can be marked with, much like page protections in the user +program address space. Such platforms can and do report errors in the +kernel logs when the PCI controller hardware detects violation of the +permission setting. + +Only streaming mappings specify a direction, consistent mappings +implicitly have a direction attribute setting of +PCI_DMA_BIDIRECTIONAL. + +The SCSI subsystem tells you the direction to use in the +'sc_data_direction' member of the SCSI command your driver is +working on. + +For Networking drivers, it's a rather simple affair. For transmit +packets, map/unmap them with the PCI_DMA_TODEVICE direction +specifier. For receive packets, just the opposite, map/unmap them +with the PCI_DMA_FROMDEVICE direction specifier. + + Using Streaming DMA mappings + +The streaming DMA mapping routines can be called from interrupt +context. There are two versions of each map/unmap, one which will +map/unmap a single memory region, and one which will map/unmap a +scatterlist. + +To map a single region, you do: + + struct pci_dev *pdev = mydev->pdev; + dma_addr_t dma_handle; + void *addr = buffer->ptr; + size_t size = buffer->len; + + dma_handle = pci_map_single(pdev, addr, size, direction); + +and to unmap it: + + pci_unmap_single(pdev, dma_handle, size, direction); + +You should call pci_unmap_single when the DMA activity is finished, e.g. +from the interrupt which told you that the DMA transfer is done. + +Using cpu pointers like this for single mappings has a disadvantage, +you cannot reference HIGHMEM memory in this way. Thus, there is a +map/unmap interface pair akin to pci_{map,unmap}_single. These +interfaces deal with page/offset pairs instead of cpu pointers. +Specifically: + + struct pci_dev *pdev = mydev->pdev; + dma_addr_t dma_handle; + struct page *page = buffer->page; + unsigned long offset = buffer->offset; + size_t size = buffer->len; + + dma_handle = pci_map_page(pdev, page, offset, size, direction); + + ... + + pci_unmap_page(pdev, dma_handle, size, direction); + +Here, "offset" means byte offset within the given page. + +With scatterlists, you map a region gathered from several regions by: + + int i, count = pci_map_sg(pdev, sglist, nents, direction); + struct scatterlist *sg; + + for_each_sg(sglist, sg, count, i) { + hw_address[i] = sg_dma_address(sg); + hw_len[i] = sg_dma_len(sg); + } + +where nents is the number of entries in the sglist. + +The implementation is free to merge several consecutive sglist entries +into one (e.g. if DMA mapping is done with PAGE_SIZE granularity, any +consecutive sglist entries can be merged into one provided the first one +ends and the second one starts on a page boundary - in fact this is a huge +advantage for cards which either cannot do scatter-gather or have very +limited number of scatter-gather entries) and returns the actual number +of sg entries it mapped them to. On failure 0 is returned. + +Then you should loop count times (note: this can be less than nents times) +and use sg_dma_address() and sg_dma_len() macros where you previously +accessed sg->address and sg->length as shown above. + +To unmap a scatterlist, just call: + + pci_unmap_sg(pdev, sglist, nents, direction); + +Again, make sure DMA activity has already finished. + +PLEASE NOTE: The 'nents' argument to the pci_unmap_sg call must be + the _same_ one you passed into the pci_map_sg call, + it should _NOT_ be the 'count' value _returned_ from the + pci_map_sg call. + +Every pci_map_{single,sg} call should have its pci_unmap_{single,sg} +counterpart, because the bus address space is a shared resource (although +in some ports the mapping is per each BUS so less devices contend for the +same bus address space) and you could render the machine unusable by eating +all bus addresses. + +If you need to use the same streaming DMA region multiple times and touch +the data in between the DMA transfers, the buffer needs to be synced +properly in order for the cpu and device to see the most uptodate and +correct copy of the DMA buffer. + +So, firstly, just map it with pci_map_{single,sg}, and after each DMA +transfer call either: + + pci_dma_sync_single_for_cpu(pdev, dma_handle, size, direction); + +or: + + pci_dma_sync_sg_for_cpu(pdev, sglist, nents, direction); + +as appropriate. + +Then, if you wish to let the device get at the DMA area again, +finish accessing the data with the cpu, and then before actually +giving the buffer to the hardware call either: + + pci_dma_sync_single_for_device(pdev, dma_handle, size, direction); + +or: + + pci_dma_sync_sg_for_device(dev, sglist, nents, direction); + +as appropriate. + +After the last DMA transfer call one of the DMA unmap routines +pci_unmap_{single,sg}. If you don't touch the data from the first pci_map_* +call till pci_unmap_*, then you don't have to call the pci_dma_sync_* +routines at all. + +Here is pseudo code which shows a situation in which you would need +to use the pci_dma_sync_*() interfaces. + + my_card_setup_receive_buffer(struct my_card *cp, char *buffer, int len) + { + dma_addr_t mapping; + + mapping = pci_map_single(cp->pdev, buffer, len, PCI_DMA_FROMDEVICE); + + cp->rx_buf = buffer; + cp->rx_len = len; + cp->rx_dma = mapping; + + give_rx_buf_to_card(cp); + } + + ... + + my_card_interrupt_handler(int irq, void *devid, struct pt_regs *regs) + { + struct my_card *cp = devid; + + ... + if (read_card_status(cp) == RX_BUF_TRANSFERRED) { + struct my_card_header *hp; + + /* Examine the header to see if we wish + * to accept the data. But synchronize + * the DMA transfer with the CPU first + * so that we see updated contents. + */ + pci_dma_sync_single_for_cpu(cp->pdev, cp->rx_dma, + cp->rx_len, + PCI_DMA_FROMDEVICE); + + /* Now it is safe to examine the buffer. */ + hp = (struct my_card_header *) cp->rx_buf; + if (header_is_ok(hp)) { + pci_unmap_single(cp->pdev, cp->rx_dma, cp->rx_len, + PCI_DMA_FROMDEVICE); + pass_to_upper_layers(cp->rx_buf); + make_and_setup_new_rx_buf(cp); + } else { + /* Just sync the buffer and give it back + * to the card. + */ + pci_dma_sync_single_for_device(cp->pdev, + cp->rx_dma, + cp->rx_len, + PCI_DMA_FROMDEVICE); + give_rx_buf_to_card(cp); + } + } + } + +Drivers converted fully to this interface should not use virt_to_bus any +longer, nor should they use bus_to_virt. Some drivers have to be changed a +little bit, because there is no longer an equivalent to bus_to_virt in the +dynamic DMA mapping scheme - you have to always store the DMA addresses +returned by the pci_alloc_consistent, pci_pool_alloc, and pci_map_single +calls (pci_map_sg stores them in the scatterlist itself if the platform +supports dynamic DMA mapping in hardware) in your driver structures and/or +in the card registers. + +All PCI drivers should be using these interfaces with no exceptions. +It is planned to completely remove virt_to_bus() and bus_to_virt() as +they are entirely deprecated. Some ports already do not provide these +as it is impossible to correctly support them. + + Optimizing Unmap State Space Consumption + +On many platforms, pci_unmap_{single,page}() is simply a nop. +Therefore, keeping track of the mapping address and length is a waste +of space. Instead of filling your drivers up with ifdefs and the like +to "work around" this (which would defeat the whole purpose of a +portable API) the following facilities are provided. + +Actually, instead of describing the macros one by one, we'll +transform some example code. + +1) Use DECLARE_PCI_UNMAP_{ADDR,LEN} in state saving structures. + Example, before: + + struct ring_state { + struct sk_buff *skb; + dma_addr_t mapping; + __u32 len; + }; + + after: + + struct ring_state { + struct sk_buff *skb; + DECLARE_PCI_UNMAP_ADDR(mapping) + DECLARE_PCI_UNMAP_LEN(len) + }; + + NOTE: DO NOT put a semicolon at the end of the DECLARE_*() + macro. + +2) Use pci_unmap_{addr,len}_set to set these values. + Example, before: + + ringp->mapping = FOO; + ringp->len = BAR; + + after: + + pci_unmap_addr_set(ringp, mapping, FOO); + pci_unmap_len_set(ringp, len, BAR); + +3) Use pci_unmap_{addr,len} to access these values. + Example, before: + + pci_unmap_single(pdev, ringp->mapping, ringp->len, + PCI_DMA_FROMDEVICE); + + after: + + pci_unmap_single(pdev, + pci_unmap_addr(ringp, mapping), + pci_unmap_len(ringp, len), + PCI_DMA_FROMDEVICE); + +It really should be self-explanatory. We treat the ADDR and LEN +separately, because it is possible for an implementation to only +need the address in order to perform the unmap operation. + + Platform Issues + +If you are just writing drivers for Linux and do not maintain +an architecture port for the kernel, you can safely skip down +to "Closing". + +1) Struct scatterlist requirements. + + Struct scatterlist must contain, at a minimum, the following + members: + + struct page *page; + unsigned int offset; + unsigned int length; + + The base address is specified by a "page+offset" pair. + + Previous versions of struct scatterlist contained a "void *address" + field that was sometimes used instead of page+offset. As of Linux + 2.5., page+offset is always used, and the "address" field has been + deleted. + +2) More to come... + + Handling Errors + +DMA address space is limited on some architectures and an allocation +failure can be determined by: + +- checking if pci_alloc_consistent returns NULL or pci_map_sg returns 0 + +- checking the returned dma_addr_t of pci_map_single and pci_map_page + by using pci_dma_mapping_error(): + + dma_addr_t dma_handle; + + dma_handle = pci_map_single(pdev, addr, size, direction); + if (pci_dma_mapping_error(pdev, dma_handle)) { + /* + * reduce current DMA mapping usage, + * delay and try again later or + * reset driver. + */ + } + + Closing + +This document, and the API itself, would not be in it's current +form without the feedback and suggestions from numerous individuals. +We would like to specifically mention, in no particular order, the +following people: + + Russell King <rmk@arm.linux.org.uk> + Leo Dagum <dagum@barrel.engr.sgi.com> + Ralf Baechle <ralf@oss.sgi.com> + Grant Grundler <grundler@cup.hp.com> + Jay Estabrook <Jay.Estabrook@compaq.com> + Thomas Sailer <sailer@ife.ee.ethz.ch> + Andrea Arcangeli <andrea@suse.de> + Jens Axboe <jens.axboe@oracle.com> + David Mosberger-Tang <davidm@hpl.hp.com> diff --git a/Documentation/PCI/PCIEBUS-HOWTO.txt b/Documentation/PCI/PCIEBUS-HOWTO.txt new file mode 100644 index 00000000000..6bd5f372ade --- /dev/null +++ b/Documentation/PCI/PCIEBUS-HOWTO.txt @@ -0,0 +1,217 @@ + The PCI Express Port Bus Driver Guide HOWTO + Tom L Nguyen tom.l.nguyen@intel.com + 11/03/2004 + +1. About this guide + +This guide describes the basics of the PCI Express Port Bus driver +and provides information on how to enable the service drivers to +register/unregister with the PCI Express Port Bus Driver. + +2. Copyright 2004 Intel Corporation + +3. What is the PCI Express Port Bus Driver + +A PCI Express Port is a logical PCI-PCI Bridge structure. There +are two types of PCI Express Port: the Root Port and the Switch +Port. The Root Port originates a PCI Express link from a PCI Express +Root Complex and the Switch Port connects PCI Express links to +internal logical PCI buses. The Switch Port, which has its secondary +bus representing the switch's internal routing logic, is called the +switch's Upstream Port. The switch's Downstream Port is bridging from +switch's internal routing bus to a bus representing the downstream +PCI Express link from the PCI Express Switch. + +A PCI Express Port can provide up to four distinct functions, +referred to in this document as services, depending on its port type. +PCI Express Port's services include native hotplug support (HP), +power management event support (PME), advanced error reporting +support (AER), and virtual channel support (VC). These services may +be handled by a single complex driver or be individually distributed +and handled by corresponding service drivers. + +4. Why use the PCI Express Port Bus Driver? + +In existing Linux kernels, the Linux Device Driver Model allows a +physical device to be handled by only a single driver. The PCI +Express Port is a PCI-PCI Bridge device with multiple distinct +services. To maintain a clean and simple solution each service +may have its own software service driver. In this case several +service drivers will compete for a single PCI-PCI Bridge device. +For example, if the PCI Express Root Port native hotplug service +driver is loaded first, it claims a PCI-PCI Bridge Root Port. The +kernel therefore does not load other service drivers for that Root +Port. In other words, it is impossible to have multiple service +drivers load and run on a PCI-PCI Bridge device simultaneously +using the current driver model. + +To enable multiple service drivers running simultaneously requires +having a PCI Express Port Bus driver, which manages all populated +PCI Express Ports and distributes all provided service requests +to the corresponding service drivers as required. Some key +advantages of using the PCI Express Port Bus driver are listed below: + + - Allow multiple service drivers to run simultaneously on + a PCI-PCI Bridge Port device. + + - Allow service drivers implemented in an independent + staged approach. + + - Allow one service driver to run on multiple PCI-PCI Bridge + Port devices. + + - Manage and distribute resources of a PCI-PCI Bridge Port + device to requested service drivers. + +5. Configuring the PCI Express Port Bus Driver vs. Service Drivers + +5.1 Including the PCI Express Port Bus Driver Support into the Kernel + +Including the PCI Express Port Bus driver depends on whether the PCI +Express support is included in the kernel config. The kernel will +automatically include the PCI Express Port Bus driver as a kernel +driver when the PCI Express support is enabled in the kernel. + +5.2 Enabling Service Driver Support + +PCI device drivers are implemented based on Linux Device Driver Model. +All service drivers are PCI device drivers. As discussed above, it is +impossible to load any service driver once the kernel has loaded the +PCI Express Port Bus Driver. To meet the PCI Express Port Bus Driver +Model requires some minimal changes on existing service drivers that +imposes no impact on the functionality of existing service drivers. + +A service driver is required to use the two APIs shown below to +register its service with the PCI Express Port Bus driver (see +section 5.2.1 & 5.2.2). It is important that a service driver +initializes the pcie_port_service_driver data structure, included in +header file /include/linux/pcieport_if.h, before calling these APIs. +Failure to do so will result an identity mismatch, which prevents +the PCI Express Port Bus driver from loading a service driver. + +5.2.1 pcie_port_service_register + +int pcie_port_service_register(struct pcie_port_service_driver *new) + +This API replaces the Linux Driver Model's pci_register_driver API. A +service driver should always calls pcie_port_service_register at +module init. Note that after service driver being loaded, calls +such as pci_enable_device(dev) and pci_set_master(dev) are no longer +necessary since these calls are executed by the PCI Port Bus driver. + +5.2.2 pcie_port_service_unregister + +void pcie_port_service_unregister(struct pcie_port_service_driver *new) + +pcie_port_service_unregister replaces the Linux Driver Model's +pci_unregister_driver. It's always called by service driver when a +module exits. + +5.2.3 Sample Code + +Below is sample service driver code to initialize the port service +driver data structure. + +static struct pcie_port_service_id service_id[] = { { + .vendor = PCI_ANY_ID, + .device = PCI_ANY_ID, + .port_type = PCIE_RC_PORT, + .service_type = PCIE_PORT_SERVICE_AER, + }, { /* end: all zeroes */ } +}; + +static struct pcie_port_service_driver root_aerdrv = { + .name = (char *)device_name, + .id_table = &service_id[0], + + .probe = aerdrv_load, + .remove = aerdrv_unload, + + .suspend = aerdrv_suspend, + .resume = aerdrv_resume, +}; + +Below is a sample code for registering/unregistering a service +driver. + +static int __init aerdrv_service_init(void) +{ + int retval = 0; + + retval = pcie_port_service_register(&root_aerdrv); + if (!retval) { + /* + * FIX ME + */ + } + return retval; +} + +static void __exit aerdrv_service_exit(void) +{ + pcie_port_service_unregister(&root_aerdrv); +} + +module_init(aerdrv_service_init); +module_exit(aerdrv_service_exit); + +6. Possible Resource Conflicts + +Since all service drivers of a PCI-PCI Bridge Port device are +allowed to run simultaneously, below lists a few of possible resource +conflicts with proposed solutions. + +6.1 MSI Vector Resource + +The MSI capability structure enables a device software driver to call +pci_enable_msi to request MSI based interrupts. Once MSI interrupts +are enabled on a device, it stays in this mode until a device driver +calls pci_disable_msi to disable MSI interrupts and revert back to +INTx emulation mode. Since service drivers of the same PCI-PCI Bridge +port share the same physical device, if an individual service driver +calls pci_enable_msi/pci_disable_msi it may result unpredictable +behavior. For example, two service drivers run simultaneously on the +same physical Root Port. Both service drivers call pci_enable_msi to +request MSI based interrupts. A service driver may not know whether +any other service drivers have run on this Root Port. If either one +of them calls pci_disable_msi, it puts the other service driver +in a wrong interrupt mode. + +To avoid this situation all service drivers are not permitted to +switch interrupt mode on its device. The PCI Express Port Bus driver +is responsible for determining the interrupt mode and this should be +transparent to service drivers. Service drivers need to know only +the vector IRQ assigned to the field irq of struct pcie_device, which +is passed in when the PCI Express Port Bus driver probes each service +driver. Service drivers should use (struct pcie_device*)dev->irq to +call request_irq/free_irq. In addition, the interrupt mode is stored +in the field interrupt_mode of struct pcie_device. + +6.2 MSI-X Vector Resources + +Similar to the MSI a device driver for an MSI-X capable device can +call pci_enable_msix to request MSI-X interrupts. All service drivers +are not permitted to switch interrupt mode on its device. The PCI +Express Port Bus driver is responsible for determining the interrupt +mode and this should be transparent to service drivers. Any attempt +by service driver to call pci_enable_msix/pci_disable_msix may +result unpredictable behavior. Service drivers should use +(struct pcie_device*)dev->irq and call request_irq/free_irq. + +6.3 PCI Memory/IO Mapped Regions + +Service drivers for PCI Express Power Management (PME), Advanced +Error Reporting (AER), Hot-Plug (HP) and Virtual Channel (VC) access +PCI configuration space on the PCI Express port. In all cases the +registers accessed are independent of each other. This patch assumes +that all service drivers will be well behaved and not overwrite +other service driver's configuration settings. + +6.4 PCI Config Registers + +Each service driver runs its PCI config operations on its own +capability structure except the PCI Express capability structure, in +which Root Control register and Device Control register are shared +between PME and AER. This patch assumes that all service drivers +will be well behaved and not overwrite other service driver's +configuration settings. diff --git a/Documentation/PCI/pci-error-recovery.txt b/Documentation/PCI/pci-error-recovery.txt new file mode 100644 index 00000000000..e83f2ea7641 --- /dev/null +++ b/Documentation/PCI/pci-error-recovery.txt @@ -0,0 +1,431 @@ + + PCI Error Recovery + ------------------ + February 2, 2006 + + Current document maintainer: + Linas Vepstas <linasvepstas@gmail.com> + updated by Richard Lary <rlary@us.ibm.com> + and Mike Mason <mmlnx@us.ibm.com> on 27-Jul-2009 + + +Many PCI bus controllers are able to detect a variety of hardware +PCI errors on the bus, such as parity errors on the data and address +busses, as well as SERR and PERR errors. Some of the more advanced +chipsets are able to deal with these errors; these include PCI-E chipsets, +and the PCI-host bridges found on IBM Power4, Power5 and Power6-based +pSeries boxes. A typical action taken is to disconnect the affected device, +halting all I/O to it. The goal of a disconnection is to avoid system +corruption; for example, to halt system memory corruption due to DMA's +to "wild" addresses. Typically, a reconnection mechanism is also +offered, so that the affected PCI device(s) are reset and put back +into working condition. The reset phase requires coordination +between the affected device drivers and the PCI controller chip. +This document describes a generic API for notifying device drivers +of a bus disconnection, and then performing error recovery. +This API is currently implemented in the 2.6.16 and later kernels. + +Reporting and recovery is performed in several steps. First, when +a PCI hardware error has resulted in a bus disconnect, that event +is reported as soon as possible to all affected device drivers, +including multiple instances of a device driver on multi-function +cards. This allows device drivers to avoid deadlocking in spinloops, +waiting for some i/o-space register to change, when it never will. +It also gives the drivers a chance to defer incoming I/O as +needed. + +Next, recovery is performed in several stages. Most of the complexity +is forced by the need to handle multi-function devices, that is, +devices that have multiple device drivers associated with them. +In the first stage, each driver is allowed to indicate what type +of reset it desires, the choices being a simple re-enabling of I/O +or requesting a slot reset. + +If any driver requests a slot reset, that is what will be done. + +After a reset and/or a re-enabling of I/O, all drivers are +again notified, so that they may then perform any device setup/config +that may be required. After these have all completed, a final +"resume normal operations" event is sent out. + +The biggest reason for choosing a kernel-based implementation rather +than a user-space implementation was the need to deal with bus +disconnects of PCI devices attached to storage media, and, in particular, +disconnects from devices holding the root file system. If the root +file system is disconnected, a user-space mechanism would have to go +through a large number of contortions to complete recovery. Almost all +of the current Linux file systems are not tolerant of disconnection +from/reconnection to their underlying block device. By contrast, +bus errors are easy to manage in the device driver. Indeed, most +device drivers already handle very similar recovery procedures; +for example, the SCSI-generic layer already provides significant +mechanisms for dealing with SCSI bus errors and SCSI bus resets. + + +Detailed Design +--------------- +Design and implementation details below, based on a chain of +public email discussions with Ben Herrenschmidt, circa 5 April 2005. + +The error recovery API support is exposed to the driver in the form of +a structure of function pointers pointed to by a new field in struct +pci_driver. A driver that fails to provide the structure is "non-aware", +and the actual recovery steps taken are platform dependent. The +arch/powerpc implementation will simulate a PCI hotplug remove/add. + +This structure has the form: +struct pci_error_handlers +{ + int (*error_detected)(struct pci_dev *dev, enum pci_channel_state); + int (*mmio_enabled)(struct pci_dev *dev); + int (*link_reset)(struct pci_dev *dev); + int (*slot_reset)(struct pci_dev *dev); + void (*resume)(struct pci_dev *dev); +}; + +The possible channel states are: +enum pci_channel_state { + pci_channel_io_normal, /* I/O channel is in normal state */ + pci_channel_io_frozen, /* I/O to channel is blocked */ + pci_channel_io_perm_failure, /* PCI card is dead */ +}; + +Possible return values are: +enum pci_ers_result { + PCI_ERS_RESULT_NONE, /* no result/none/not supported in device driver */ + PCI_ERS_RESULT_CAN_RECOVER, /* Device driver can recover without slot reset */ + PCI_ERS_RESULT_NEED_RESET, /* Device driver wants slot to be reset. */ + PCI_ERS_RESULT_DISCONNECT, /* Device has completely failed, is unrecoverable */ + PCI_ERS_RESULT_RECOVERED, /* Device driver is fully recovered and operational */ +}; + +A driver does not have to implement all of these callbacks; however, +if it implements any, it must implement error_detected(). If a callback +is not implemented, the corresponding feature is considered unsupported. +For example, if mmio_enabled() and resume() aren't there, then it +is assumed that the driver is not doing any direct recovery and requires +a slot reset. If link_reset() is not implemented, the card is assumed to +not care about link resets. Typically a driver will want to know about +a slot_reset(). + +The actual steps taken by a platform to recover from a PCI error +event will be platform-dependent, but will follow the general +sequence described below. + +STEP 0: Error Event +------------------- +A PCI bus error is detected by the PCI hardware. On powerpc, the slot +is isolated, in that all I/O is blocked: all reads return 0xffffffff, +all writes are ignored. + + +STEP 1: Notification +-------------------- +Platform calls the error_detected() callback on every instance of +every driver affected by the error. + +At this point, the device might not be accessible anymore, depending on +the platform (the slot will be isolated on powerpc). The driver may +already have "noticed" the error because of a failing I/O, but this +is the proper "synchronization point", that is, it gives the driver +a chance to cleanup, waiting for pending stuff (timers, whatever, etc...) +to complete; it can take semaphores, schedule, etc... everything but +touch the device. Within this function and after it returns, the driver +shouldn't do any new IOs. Called in task context. This is sort of a +"quiesce" point. See note about interrupts at the end of this doc. + +All drivers participating in this system must implement this call. +The driver must return one of the following result codes: + - PCI_ERS_RESULT_CAN_RECOVER: + Driver returns this if it thinks it might be able to recover + the HW by just banging IOs or if it wants to be given + a chance to extract some diagnostic information (see + mmio_enable, below). + - PCI_ERS_RESULT_NEED_RESET: + Driver returns this if it can't recover without a + slot reset. + - PCI_ERS_RESULT_DISCONNECT: + Driver returns this if it doesn't want to recover at all. + +The next step taken will depend on the result codes returned by the +drivers. + +If all drivers on the segment/slot return PCI_ERS_RESULT_CAN_RECOVER, +then the platform should re-enable IOs on the slot (or do nothing in +particular, if the platform doesn't isolate slots), and recovery +proceeds to STEP 2 (MMIO Enable). + +If any driver requested a slot reset (by returning PCI_ERS_RESULT_NEED_RESET), +then recovery proceeds to STEP 4 (Slot Reset). + +If the platform is unable to recover the slot, the next step +is STEP 6 (Permanent Failure). + +>>> The current powerpc implementation assumes that a device driver will +>>> *not* schedule or semaphore in this routine; the current powerpc +>>> implementation uses one kernel thread to notify all devices; +>>> thus, if one device sleeps/schedules, all devices are affected. +>>> Doing better requires complex multi-threaded logic in the error +>>> recovery implementation (e.g. waiting for all notification threads +>>> to "join" before proceeding with recovery.) This seems excessively +>>> complex and not worth implementing. + +>>> The current powerpc implementation doesn't much care if the device +>>> attempts I/O at this point, or not. I/O's will fail, returning +>>> a value of 0xff on read, and writes will be dropped. If more than +>>> EEH_MAX_FAILS I/O's are attempted to a frozen adapter, EEH +>>> assumes that the device driver has gone into an infinite loop +>>> and prints an error to syslog. A reboot is then required to +>>> get the device working again. + +STEP 2: MMIO Enabled +------------------- +The platform re-enables MMIO to the device (but typically not the +DMA), and then calls the mmio_enabled() callback on all affected +device drivers. + +This is the "early recovery" call. IOs are allowed again, but DMA is +not, with some restrictions. This is NOT a callback for the driver to +start operations again, only to peek/poke at the device, extract diagnostic +information, if any, and eventually do things like trigger a device local +reset or some such, but not restart operations. This callback is made if +all drivers on a segment agree that they can try to recover and if no automatic +link reset was performed by the HW. If the platform can't just re-enable IOs +without a slot reset or a link reset, it will not call this callback, and +instead will have gone directly to STEP 3 (Link Reset) or STEP 4 (Slot Reset) + +>>> The following is proposed; no platform implements this yet: +>>> Proposal: All I/O's should be done _synchronously_ from within +>>> this callback, errors triggered by them will be returned via +>>> the normal pci_check_whatever() API, no new error_detected() +>>> callback will be issued due to an error happening here. However, +>>> such an error might cause IOs to be re-blocked for the whole +>>> segment, and thus invalidate the recovery that other devices +>>> on the same segment might have done, forcing the whole segment +>>> into one of the next states, that is, link reset or slot reset. + +The driver should return one of the following result codes: + - PCI_ERS_RESULT_RECOVERED + Driver returns this if it thinks the device is fully + functional and thinks it is ready to start + normal driver operations again. There is no + guarantee that the driver will actually be + allowed to proceed, as another driver on the + same segment might have failed and thus triggered a + slot reset on platforms that support it. + + - PCI_ERS_RESULT_NEED_RESET + Driver returns this if it thinks the device is not + recoverable in it's current state and it needs a slot + reset to proceed. + + - PCI_ERS_RESULT_DISCONNECT + Same as above. Total failure, no recovery even after + reset driver dead. (To be defined more precisely) + +The next step taken depends on the results returned by the drivers. +If all drivers returned PCI_ERS_RESULT_RECOVERED, then the platform +proceeds to either STEP3 (Link Reset) or to STEP 5 (Resume Operations). + +If any driver returned PCI_ERS_RESULT_NEED_RESET, then the platform +proceeds to STEP 4 (Slot Reset) + +STEP 3: Link Reset +------------------ +The platform resets the link, and then calls the link_reset() callback +on all affected device drivers. This is a PCI-Express specific state +and is done whenever a non-fatal error has been detected that can be +"solved" by resetting the link. This call informs the driver of the +reset and the driver should check to see if the device appears to be +in working condition. + +The driver is not supposed to restart normal driver I/O operations +at this point. It should limit itself to "probing" the device to +check it's recoverability status. If all is right, then the platform +will call resume() once all drivers have ack'd link_reset(). + + Result codes: + (identical to STEP 3 (MMIO Enabled) + +The platform then proceeds to either STEP 4 (Slot Reset) or STEP 5 +(Resume Operations). + +>>> The current powerpc implementation does not implement this callback. + +STEP 4: Slot Reset +------------------ + +In response to a return value of PCI_ERS_RESULT_NEED_RESET, the +the platform will peform a slot reset on the requesting PCI device(s). +The actual steps taken by a platform to perform a slot reset +will be platform-dependent. Upon completion of slot reset, the +platform will call the device slot_reset() callback. + +Powerpc platforms implement two levels of slot reset: +soft reset(default) and fundamental(optional) reset. + +Powerpc soft reset consists of asserting the adapter #RST line and then +restoring the PCI BAR's and PCI configuration header to a state +that is equivalent to what it would be after a fresh system +power-on followed by power-on BIOS/system firmware initialization. +Soft reset is also known as hot-reset. + +Powerpc fundamental reset is supported by PCI Express cards only +and results in device's state machines, hardware logic, port states and +configuration registers to initialize to their default conditions. + +For most PCI devices, a soft reset will be sufficient for recovery. +Optional fundamental reset is provided to support a limited number +of PCI Express PCI devices for which a soft reset is not sufficient +for recovery. + +If the platform supports PCI hotplug, then the reset might be +performed by toggling the slot electrical power off/on. + +It is important for the platform to restore the PCI config space +to the "fresh poweron" state, rather than the "last state". After +a slot reset, the device driver will almost always use its standard +device initialization routines, and an unusual config space setup +may result in hung devices, kernel panics, or silent data corruption. + +This call gives drivers the chance to re-initialize the hardware +(re-download firmware, etc.). At this point, the driver may assume +that the card is in a fresh state and is fully functional. The slot +is unfrozen and the driver has full access to PCI config space, +memory mapped I/O space and DMA. Interrupts (Legacy, MSI, or MSI-X) +will also be available. + +Drivers should not restart normal I/O processing operations +at this point. If all device drivers report success on this +callback, the platform will call resume() to complete the sequence, +and let the driver restart normal I/O processing. + +A driver can still return a critical failure for this function if +it can't get the device operational after reset. If the platform +previously tried a soft reset, it might now try a hard reset (power +cycle) and then call slot_reset() again. It the device still can't +be recovered, there is nothing more that can be done; the platform +will typically report a "permanent failure" in such a case. The +device will be considered "dead" in this case. + +Drivers for multi-function cards will need to coordinate among +themselves as to which driver instance will perform any "one-shot" +or global device initialization. For example, the Symbios sym53cxx2 +driver performs device init only from PCI function 0: + ++ if (PCI_FUNC(pdev->devfn) == 0) ++ sym_reset_scsi_bus(np, 0); + + Result codes: + - PCI_ERS_RESULT_DISCONNECT + Same as above. + +Drivers for PCI Express cards that require a fundamental reset must +set the needs_freset bit in the pci_dev structure in their probe function. +For example, the QLogic qla2xxx driver sets the needs_freset bit for certain +PCI card types: + ++ /* Set EEH reset type to fundamental if required by hba */ ++ if (IS_QLA24XX(ha) || IS_QLA25XX(ha) || IS_QLA81XX(ha)) ++ pdev->needs_freset = 1; ++ + +Platform proceeds either to STEP 5 (Resume Operations) or STEP 6 (Permanent +Failure). + +>>> The current powerpc implementation does not try a power-cycle +>>> reset if the driver returned PCI_ERS_RESULT_DISCONNECT. +>>> However, it probably should. + + +STEP 5: Resume Operations +------------------------- +The platform will call the resume() callback on all affected device +drivers if all drivers on the segment have returned +PCI_ERS_RESULT_RECOVERED from one of the 3 previous callbacks. +The goal of this callback is to tell the driver to restart activity, +that everything is back and running. This callback does not return +a result code. + +At this point, if a new error happens, the platform will restart +a new error recovery sequence. + +STEP 6: Permanent Failure +------------------------- +A "permanent failure" has occurred, and the platform cannot recover +the device. The platform will call error_detected() with a +pci_channel_state value of pci_channel_io_perm_failure. + +The device driver should, at this point, assume the worst. It should +cancel all pending I/O, refuse all new I/O, returning -EIO to +higher layers. The device driver should then clean up all of its +memory and remove itself from kernel operations, much as it would +during system shutdown. + +The platform will typically notify the system operator of the +permanent failure in some way. If the device is hotplug-capable, +the operator will probably want to remove and replace the device. +Note, however, not all failures are truly "permanent". Some are +caused by over-heating, some by a poorly seated card. Many +PCI error events are caused by software bugs, e.g. DMA's to +wild addresses or bogus split transactions due to programming +errors. See the discussion in powerpc/eeh-pci-error-recovery.txt +for additional detail on real-life experience of the causes of +software errors. + + +Conclusion; General Remarks +--------------------------- +The way the callbacks are called is platform policy. A platform with +no slot reset capability may want to just "ignore" drivers that can't +recover (disconnect them) and try to let other cards on the same segment +recover. Keep in mind that in most real life cases, though, there will +be only one driver per segment. + +Now, a note about interrupts. If you get an interrupt and your +device is dead or has been isolated, there is a problem :) +The current policy is to turn this into a platform policy. +That is, the recovery API only requires that: + + - There is no guarantee that interrupt delivery can proceed from any +device on the segment starting from the error detection and until the +slot_reset callback is called, at which point interrupts are expected +to be fully operational. + + - There is no guarantee that interrupt delivery is stopped, that is, +a driver that gets an interrupt after detecting an error, or that detects +an error within the interrupt handler such that it prevents proper +ack'ing of the interrupt (and thus removal of the source) should just +return IRQ_NOTHANDLED. It's up to the platform to deal with that +condition, typically by masking the IRQ source during the duration of +the error handling. It is expected that the platform "knows" which +interrupts are routed to error-management capable slots and can deal +with temporarily disabling that IRQ number during error processing (this +isn't terribly complex). That means some IRQ latency for other devices +sharing the interrupt, but there is simply no other way. High end +platforms aren't supposed to share interrupts between many devices +anyway :) + +>>> Implementation details for the powerpc platform are discussed in +>>> the file Documentation/powerpc/eeh-pci-error-recovery.txt + +>>> As of this writing, there is a growing list of device drivers with +>>> patches implementing error recovery. Not all of these patches are in +>>> mainline yet. These may be used as "examples": +>>> +>>> drivers/scsi/ipr +>>> drivers/scsi/sym53c8xx_2 +>>> drivers/scsi/qla2xxx +>>> drivers/scsi/lpfc +>>> drivers/next/bnx2.c +>>> drivers/next/e100.c +>>> drivers/net/e1000 +>>> drivers/net/e1000e +>>> drivers/net/ixgb +>>> drivers/net/ixgbe +>>> drivers/net/cxgb3 +>>> drivers/net/s2io.c +>>> drivers/net/qlge + +The End +------- diff --git a/Documentation/PCI/pci-iov-howto.txt b/Documentation/PCI/pci-iov-howto.txt new file mode 100644 index 00000000000..fc73ef5d65b --- /dev/null +++ b/Documentation/PCI/pci-iov-howto.txt @@ -0,0 +1,99 @@ + PCI Express I/O Virtualization Howto + Copyright (C) 2009 Intel Corporation + Yu Zhao <yu.zhao@intel.com> + + +1. Overview + +1.1 What is SR-IOV + +Single Root I/O Virtualization (SR-IOV) is a PCI Express Extended +capability which makes one physical device appear as multiple virtual +devices. The physical device is referred to as Physical Function (PF) +while the virtual devices are referred to as Virtual Functions (VF). +Allocation of the VF can be dynamically controlled by the PF via +registers encapsulated in the capability. By default, this feature is +not enabled and the PF behaves as traditional PCIe device. Once it's +turned on, each VF's PCI configuration space can be accessed by its own +Bus, Device and Function Number (Routing ID). And each VF also has PCI +Memory Space, which is used to map its register set. VF device driver +operates on the register set so it can be functional and appear as a +real existing PCI device. + +2. User Guide + +2.1 How can I enable SR-IOV capability + +The device driver (PF driver) will control the enabling and disabling +of the capability via API provided by SR-IOV core. If the hardware +has SR-IOV capability, loading its PF driver would enable it and all +VFs associated with the PF. + +2.2 How can I use the Virtual Functions + +The VF is treated as hot-plugged PCI devices in the kernel, so they +should be able to work in the same way as real PCI devices. The VF +requires device driver that is same as a normal PCI device's. + +3. Developer Guide + +3.1 SR-IOV API + +To enable SR-IOV capability: + int pci_enable_sriov(struct pci_dev *dev, int nr_virtfn); + 'nr_virtfn' is number of VFs to be enabled. + +To disable SR-IOV capability: + void pci_disable_sriov(struct pci_dev *dev); + +To notify SR-IOV core of Virtual Function Migration: + irqreturn_t pci_sriov_migration(struct pci_dev *dev); + +3.2 Usage example + +Following piece of code illustrates the usage of the SR-IOV API. + +static int __devinit dev_probe(struct pci_dev *dev, const struct pci_device_id *id) +{ + pci_enable_sriov(dev, NR_VIRTFN); + + ... + + return 0; +} + +static void __devexit dev_remove(struct pci_dev *dev) +{ + pci_disable_sriov(dev); + + ... +} + +static int dev_suspend(struct pci_dev *dev, pm_message_t state) +{ + ... + + return 0; +} + +static int dev_resume(struct pci_dev *dev) +{ + ... + + return 0; +} + +static void dev_shutdown(struct pci_dev *dev) +{ + ... +} + +static struct pci_driver dev_driver = { + .name = "SR-IOV Physical Function driver", + .id_table = dev_id_table, + .probe = dev_probe, + .remove = __devexit_p(dev_remove), + .suspend = dev_suspend, + .resume = dev_resume, + .shutdown = dev_shutdown, +}; diff --git a/Documentation/PCI/pci.txt b/Documentation/PCI/pci.txt new file mode 100644 index 00000000000..7f6de6ea5b4 --- /dev/null +++ b/Documentation/PCI/pci.txt @@ -0,0 +1,651 @@ + + How To Write Linux PCI Drivers + + by Martin Mares <mj@ucw.cz> on 07-Feb-2000 + updated by Grant Grundler <grundler@parisc-linux.org> on 23-Dec-2006 + +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +The world of PCI is vast and full of (mostly unpleasant) surprises. +Since each CPU architecture implements different chip-sets and PCI devices +have different requirements (erm, "features"), the result is the PCI support +in the Linux kernel is not as trivial as one would wish. This short paper +tries to introduce all potential driver authors to Linux APIs for +PCI device drivers. + +A more complete resource is the third edition of "Linux Device Drivers" +by Jonathan Corbet, Alessandro Rubini, and Greg Kroah-Hartman. +LDD3 is available for free (under Creative Commons License) from: + + http://lwn.net/Kernel/LDD3/ + +However, keep in mind that all documents are subject to "bit rot". +Refer to the source code if things are not working as described here. + +Please send questions/comments/patches about Linux PCI API to the +"Linux PCI" <linux-pci@atrey.karlin.mff.cuni.cz> mailing list. + + + +0. Structure of PCI drivers +~~~~~~~~~~~~~~~~~~~~~~~~~~~ +PCI drivers "discover" PCI devices in a system via pci_register_driver(). +Actually, it's the other way around. When the PCI generic code discovers +a new device, the driver with a matching "description" will be notified. +Details on this below. + +pci_register_driver() leaves most of the probing for devices to +the PCI layer and supports online insertion/removal of devices [thus +supporting hot-pluggable PCI, CardBus, and Express-Card in a single driver]. +pci_register_driver() call requires passing in a table of function +pointers and thus dictates the high level structure of a driver. + +Once the driver knows about a PCI device and takes ownership, the +driver generally needs to perform the following initialization: + + Enable the device + Request MMIO/IOP resources + Set the DMA mask size (for both coherent and streaming DMA) + Allocate and initialize shared control data (pci_allocate_coherent()) + Access device configuration space (if needed) + Register IRQ handler (request_irq()) + Initialize non-PCI (i.e. LAN/SCSI/etc parts of the chip) + Enable DMA/processing engines + +When done using the device, and perhaps the module needs to be unloaded, +the driver needs to take the follow steps: + Disable the device from generating IRQs + Release the IRQ (free_irq()) + Stop all DMA activity + Release DMA buffers (both streaming and coherent) + Unregister from other subsystems (e.g. scsi or netdev) + Release MMIO/IOP resources + Disable the device + +Most of these topics are covered in the following sections. +For the rest look at LDD3 or <linux/pci.h> . + +If the PCI subsystem is not configured (CONFIG_PCI is not set), most of +the PCI functions described below are defined as inline functions either +completely empty or just returning an appropriate error codes to avoid +lots of ifdefs in the drivers. + + + +1. pci_register_driver() call +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +PCI device drivers call pci_register_driver() during their +initialization with a pointer to a structure describing the driver +(struct pci_driver): + + field name Description + ---------- ------------------------------------------------------ + id_table Pointer to table of device ID's the driver is + interested in. Most drivers should export this + table using MODULE_DEVICE_TABLE(pci,...). + + probe This probing function gets called (during execution + of pci_register_driver() for already existing + devices or later if a new device gets inserted) for + all PCI devices which match the ID table and are not + "owned" by the other drivers yet. This function gets + passed a "struct pci_dev *" for each device whose + entry in the ID table matches the device. The probe + function returns zero when the driver chooses to + take "ownership" of the device or an error code + (negative number) otherwise. + The probe function always gets called from process + context, so it can sleep. + + remove The remove() function gets called whenever a device + being handled by this driver is removed (either during + deregistration of the driver or when it's manually + pulled out of a hot-pluggable slot). + The remove function always gets called from process + context, so it can sleep. + + suspend Put device into low power state. + suspend_late Put device into low power state. + + resume_early Wake device from low power state. + resume Wake device from low power state. + + (Please see Documentation/power/pci.txt for descriptions + of PCI Power Management and the related functions.) + + shutdown Hook into reboot_notifier_list (kernel/sys.c). + Intended to stop any idling DMA operations. + Useful for enabling wake-on-lan (NIC) or changing + the power state of a device before reboot. + e.g. drivers/net/e100.c. + + err_handler See Documentation/PCI/pci-error-recovery.txt + + +The ID table is an array of struct pci_device_id entries ending with an +all-zero entry; use of the macro DEFINE_PCI_DEVICE_TABLE is the preferred +method of declaring the table. Each entry consists of: + + vendor,device Vendor and device ID to match (or PCI_ANY_ID) + + subvendor, Subsystem vendor and device ID to match (or PCI_ANY_ID) + subdevice, + + class Device class, subclass, and "interface" to match. + See Appendix D of the PCI Local Bus Spec or + include/linux/pci_ids.h for a full list of classes. + Most drivers do not need to specify class/class_mask + as vendor/device is normally sufficient. + + class_mask limit which sub-fields of the class field are compared. + See drivers/scsi/sym53c8xx_2/ for example of usage. + + driver_data Data private to the driver. + Most drivers don't need to use driver_data field. + Best practice is to use driver_data as an index + into a static list of equivalent device types, + instead of using it as a pointer. + + +Most drivers only need PCI_DEVICE() or PCI_DEVICE_CLASS() to set up +a pci_device_id table. + +New PCI IDs may be added to a device driver pci_ids table at runtime +as shown below: + +echo "vendor device subvendor subdevice class class_mask driver_data" > \ +/sys/bus/pci/drivers/{driver}/new_id + +All fields are passed in as hexadecimal values (no leading 0x). +The vendor and device fields are mandatory, the others are optional. Users +need pass only as many optional fields as necessary: + o subvendor and subdevice fields default to PCI_ANY_ID (FFFFFFFF) + o class and classmask fields default to 0 + o driver_data defaults to 0UL. + +Note that driver_data must match the value used by any of the pci_device_id +entries defined in the driver. This makes the driver_data field mandatory +if all the pci_device_id entries have a non-zero driver_data value. + +Once added, the driver probe routine will be invoked for any unclaimed +PCI devices listed in its (newly updated) pci_ids list. + +When the driver exits, it just calls pci_unregister_driver() and the PCI layer +automatically calls the remove hook for all devices handled by the driver. + + +1.1 "Attributes" for driver functions/data + +Please mark the initialization and cleanup functions where appropriate +(the corresponding macros are defined in <linux/init.h>): + + __init Initialization code. Thrown away after the driver + initializes. + __exit Exit code. Ignored for non-modular drivers. + + + __devinit Device initialization code. + Identical to __init if the kernel is not compiled + with CONFIG_HOTPLUG, normal function otherwise. + __devexit The same for __exit. + +Tips on when/where to use the above attributes: + o The module_init()/module_exit() functions (and all + initialization functions called _only_ from these) + should be marked __init/__exit. + + o Do not mark the struct pci_driver. + + o The ID table array should be marked __devinitconst; this is done + automatically if the table is declared with DEFINE_PCI_DEVICE_TABLE(). + + o The probe() and remove() functions should be marked __devinit + and __devexit respectively. All initialization functions + exclusively called by the probe() routine, can be marked __devinit. + Ditto for remove() and __devexit. + + o If mydriver_remove() is marked with __devexit(), then all address + references to mydriver_remove must use __devexit_p(mydriver_remove) + (in the struct pci_driver declaration for example). + __devexit_p() will generate the function name _or_ NULL if the + function will be discarded. For an example, see drivers/net/tg3.c. + + o Do NOT mark a function if you are not sure which mark to use. + Better to not mark the function than mark the function wrong. + + + +2. How to find PCI devices manually +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +PCI drivers should have a really good reason for not using the +pci_register_driver() interface to search for PCI devices. +The main reason PCI devices are controlled by multiple drivers +is because one PCI device implements several different HW services. +E.g. combined serial/parallel port/floppy controller. + +A manual search may be performed using the following constructs: + +Searching by vendor and device ID: + + struct pci_dev *dev = NULL; + while (dev = pci_get_device(VENDOR_ID, DEVICE_ID, dev)) + configure_device(dev); + +Searching by class ID (iterate in a similar way): + + pci_get_class(CLASS_ID, dev) + +Searching by both vendor/device and subsystem vendor/device ID: + + pci_get_subsys(VENDOR_ID,DEVICE_ID, SUBSYS_VENDOR_ID, SUBSYS_DEVICE_ID, dev). + +You can use the constant PCI_ANY_ID as a wildcard replacement for +VENDOR_ID or DEVICE_ID. This allows searching for any device from a +specific vendor, for example. + +These functions are hotplug-safe. They increment the reference count on +the pci_dev that they return. You must eventually (possibly at module unload) +decrement the reference count on these devices by calling pci_dev_put(). + + + +3. Device Initialization Steps +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +As noted in the introduction, most PCI drivers need the following steps +for device initialization: + + Enable the device + Request MMIO/IOP resources + Set the DMA mask size (for both coherent and streaming DMA) + Allocate and initialize shared control data (pci_allocate_coherent()) + Access device configuration space (if needed) + Register IRQ handler (request_irq()) + Initialize non-PCI (i.e. LAN/SCSI/etc parts of the chip) + Enable DMA/processing engines. + +The driver can access PCI config space registers at any time. +(Well, almost. When running BIST, config space can go away...but +that will just result in a PCI Bus Master Abort and config reads +will return garbage). + + +3.1 Enable the PCI device +~~~~~~~~~~~~~~~~~~~~~~~~~ +Before touching any device registers, the driver needs to enable +the PCI device by calling pci_enable_device(). This will: + o wake up the device if it was in suspended state, + o allocate I/O and memory regions of the device (if BIOS did not), + o allocate an IRQ (if BIOS did not). + +NOTE: pci_enable_device() can fail! Check the return value. + +[ OS BUG: we don't check resource allocations before enabling those + resources. The sequence would make more sense if we called + pci_request_resources() before calling pci_enable_device(). + Currently, the device drivers can't detect the bug when when two + devices have been allocated the same range. This is not a common + problem and unlikely to get fixed soon. + + This has been discussed before but not changed as of 2.6.19: + http://lkml.org/lkml/2006/3/2/194 +] + +pci_set_master() will enable DMA by setting the bus master bit +in the PCI_COMMAND register. It also fixes the latency timer value if +it's set to something bogus by the BIOS. pci_clear_master() will +disable DMA by clearing the bus master bit. + +If the PCI device can use the PCI Memory-Write-Invalidate transaction, +call pci_set_mwi(). This enables the PCI_COMMAND bit for Mem-Wr-Inval +and also ensures that the cache line size register is set correctly. +Check the return value of pci_set_mwi() as not all architectures +or chip-sets may support Memory-Write-Invalidate. Alternatively, +if Mem-Wr-Inval would be nice to have but is not required, call +pci_try_set_mwi() to have the system do its best effort at enabling +Mem-Wr-Inval. + + +3.2 Request MMIO/IOP resources +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Memory (MMIO), and I/O port addresses should NOT be read directly +from the PCI device config space. Use the values in the pci_dev structure +as the PCI "bus address" might have been remapped to a "host physical" +address by the arch/chip-set specific kernel support. + +See Documentation/IO-mapping.txt for how to access device registers +or device memory. + +The device driver needs to call pci_request_region() to verify +no other device is already using the same address resource. +Conversely, drivers should call pci_release_region() AFTER +calling pci_disable_device(). +The idea is to prevent two devices colliding on the same address range. + +[ See OS BUG comment above. Currently (2.6.19), The driver can only + determine MMIO and IO Port resource availability _after_ calling + pci_enable_device(). ] + +Generic flavors of pci_request_region() are request_mem_region() +(for MMIO ranges) and request_region() (for IO Port ranges). +Use these for address resources that are not described by "normal" PCI +BARs. + +Also see pci_request_selected_regions() below. + + +3.3 Set the DMA mask size +~~~~~~~~~~~~~~~~~~~~~~~~~ +[ If anything below doesn't make sense, please refer to + Documentation/DMA-API.txt. This section is just a reminder that + drivers need to indicate DMA capabilities of the device and is not + an authoritative source for DMA interfaces. ] + +While all drivers should explicitly indicate the DMA capability +(e.g. 32 or 64 bit) of the PCI bus master, devices with more than +32-bit bus master capability for streaming data need the driver +to "register" this capability by calling pci_set_dma_mask() with +appropriate parameters. In general this allows more efficient DMA +on systems where System RAM exists above 4G _physical_ address. + +Drivers for all PCI-X and PCIe compliant devices must call +pci_set_dma_mask() as they are 64-bit DMA devices. + +Similarly, drivers must also "register" this capability if the device +can directly address "consistent memory" in System RAM above 4G physical +address by calling pci_set_consistent_dma_mask(). +Again, this includes drivers for all PCI-X and PCIe compliant devices. +Many 64-bit "PCI" devices (before PCI-X) and some PCI-X devices are +64-bit DMA capable for payload ("streaming") data but not control +("consistent") data. + + +3.4 Setup shared control data +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Once the DMA masks are set, the driver can allocate "consistent" (a.k.a. shared) +memory. See Documentation/DMA-API.txt for a full description of +the DMA APIs. This section is just a reminder that it needs to be done +before enabling DMA on the device. + + +3.5 Initialize device registers +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Some drivers will need specific "capability" fields programmed +or other "vendor specific" register initialized or reset. +E.g. clearing pending interrupts. + + +3.6 Register IRQ handler +~~~~~~~~~~~~~~~~~~~~~~~~ +While calling request_irq() is the last step described here, +this is often just another intermediate step to initialize a device. +This step can often be deferred until the device is opened for use. + +All interrupt handlers for IRQ lines should be registered with IRQF_SHARED +and use the devid to map IRQs to devices (remember that all PCI IRQ lines +can be shared). + +request_irq() will associate an interrupt handler and device handle +with an interrupt number. Historically interrupt numbers represent +IRQ lines which run from the PCI device to the Interrupt controller. +With MSI and MSI-X (more below) the interrupt number is a CPU "vector". + +request_irq() also enables the interrupt. Make sure the device is +quiesced and does not have any interrupts pending before registering +the interrupt handler. + +MSI and MSI-X are PCI capabilities. Both are "Message Signaled Interrupts" +which deliver interrupts to the CPU via a DMA write to a Local APIC. +The fundamental difference between MSI and MSI-X is how multiple +"vectors" get allocated. MSI requires contiguous blocks of vectors +while MSI-X can allocate several individual ones. + +MSI capability can be enabled by calling pci_enable_msi() or +pci_enable_msix() before calling request_irq(). This causes +the PCI support to program CPU vector data into the PCI device +capability registers. + +If your PCI device supports both, try to enable MSI-X first. +Only one can be enabled at a time. Many architectures, chip-sets, +or BIOSes do NOT support MSI or MSI-X and the call to pci_enable_msi/msix +will fail. This is important to note since many drivers have +two (or more) interrupt handlers: one for MSI/MSI-X and another for IRQs. +They choose which handler to register with request_irq() based on the +return value from pci_enable_msi/msix(). + +There are (at least) two really good reasons for using MSI: +1) MSI is an exclusive interrupt vector by definition. + This means the interrupt handler doesn't have to verify + its device caused the interrupt. + +2) MSI avoids DMA/IRQ race conditions. DMA to host memory is guaranteed + to be visible to the host CPU(s) when the MSI is delivered. This + is important for both data coherency and avoiding stale control data. + This guarantee allows the driver to omit MMIO reads to flush + the DMA stream. + +See drivers/infiniband/hw/mthca/ or drivers/net/tg3.c for examples +of MSI/MSI-X usage. + + + +4. PCI device shutdown +~~~~~~~~~~~~~~~~~~~~~~~ + +When a PCI device driver is being unloaded, most of the following +steps need to be performed: + + Disable the device from generating IRQs + Release the IRQ (free_irq()) + Stop all DMA activity + Release DMA buffers (both streaming and consistent) + Unregister from other subsystems (e.g. scsi or netdev) + Disable device from responding to MMIO/IO Port addresses + Release MMIO/IO Port resource(s) + + +4.1 Stop IRQs on the device +~~~~~~~~~~~~~~~~~~~~~~~~~~~ +How to do this is chip/device specific. If it's not done, it opens +the possibility of a "screaming interrupt" if (and only if) +the IRQ is shared with another device. + +When the shared IRQ handler is "unhooked", the remaining devices +using the same IRQ line will still need the IRQ enabled. Thus if the +"unhooked" device asserts IRQ line, the system will respond assuming +it was one of the remaining devices asserted the IRQ line. Since none +of the other devices will handle the IRQ, the system will "hang" until +it decides the IRQ isn't going to get handled and masks the IRQ (100,000 +iterations later). Once the shared IRQ is masked, the remaining devices +will stop functioning properly. Not a nice situation. + +This is another reason to use MSI or MSI-X if it's available. +MSI and MSI-X are defined to be exclusive interrupts and thus +are not susceptible to the "screaming interrupt" problem. + + +4.2 Release the IRQ +~~~~~~~~~~~~~~~~~~~ +Once the device is quiesced (no more IRQs), one can call free_irq(). +This function will return control once any pending IRQs are handled, +"unhook" the drivers IRQ handler from that IRQ, and finally release +the IRQ if no one else is using it. + + +4.3 Stop all DMA activity +~~~~~~~~~~~~~~~~~~~~~~~~~ +It's extremely important to stop all DMA operations BEFORE attempting +to deallocate DMA control data. Failure to do so can result in memory +corruption, hangs, and on some chip-sets a hard crash. + +Stopping DMA after stopping the IRQs can avoid races where the +IRQ handler might restart DMA engines. + +While this step sounds obvious and trivial, several "mature" drivers +didn't get this step right in the past. + + +4.4 Release DMA buffers +~~~~~~~~~~~~~~~~~~~~~~~ +Once DMA is stopped, clean up streaming DMA first. +I.e. unmap data buffers and return buffers to "upstream" +owners if there is one. + +Then clean up "consistent" buffers which contain the control data. + +See Documentation/DMA-API.txt for details on unmapping interfaces. + + +4.5 Unregister from other subsystems +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Most low level PCI device drivers support some other subsystem +like USB, ALSA, SCSI, NetDev, Infiniband, etc. Make sure your +driver isn't losing resources from that other subsystem. +If this happens, typically the symptom is an Oops (panic) when +the subsystem attempts to call into a driver that has been unloaded. + + +4.6 Disable Device from responding to MMIO/IO Port addresses +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +io_unmap() MMIO or IO Port resources and then call pci_disable_device(). +This is the symmetric opposite of pci_enable_device(). +Do not access device registers after calling pci_disable_device(). + + +4.7 Release MMIO/IO Port Resource(s) +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Call pci_release_region() to mark the MMIO or IO Port range as available. +Failure to do so usually results in the inability to reload the driver. + + + +5. How to access PCI config space +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +You can use pci_(read|write)_config_(byte|word|dword) to access the config +space of a device represented by struct pci_dev *. All these functions return 0 +when successful or an error code (PCIBIOS_...) which can be translated to a text +string by pcibios_strerror. Most drivers expect that accesses to valid PCI +devices don't fail. + +If you don't have a struct pci_dev available, you can call +pci_bus_(read|write)_config_(byte|word|dword) to access a given device +and function on that bus. + +If you access fields in the standard portion of the config header, please +use symbolic names of locations and bits declared in <linux/pci.h>. + +If you need to access Extended PCI Capability registers, just call +pci_find_capability() for the particular capability and it will find the +corresponding register block for you. + + + +6. Other interesting functions +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +pci_find_slot() Find pci_dev corresponding to given bus and + slot numbers. +pci_set_power_state() Set PCI Power Management state (0=D0 ... 3=D3) +pci_find_capability() Find specified capability in device's capability + list. +pci_resource_start() Returns bus start address for a given PCI region +pci_resource_end() Returns bus end address for a given PCI region +pci_resource_len() Returns the byte length of a PCI region +pci_set_drvdata() Set private driver data pointer for a pci_dev +pci_get_drvdata() Return private driver data pointer for a pci_dev +pci_set_mwi() Enable Memory-Write-Invalidate transactions. +pci_clear_mwi() Disable Memory-Write-Invalidate transactions. + + + +7. Miscellaneous hints +~~~~~~~~~~~~~~~~~~~~~~ + +When displaying PCI device names to the user (for example when a driver wants +to tell the user what card has it found), please use pci_name(pci_dev). + +Always refer to the PCI devices by a pointer to the pci_dev structure. +All PCI layer functions use this identification and it's the only +reasonable one. Don't use bus/slot/function numbers except for very +special purposes -- on systems with multiple primary buses their semantics +can be pretty complex. + +Don't try to turn on Fast Back to Back writes in your driver. All devices +on the bus need to be capable of doing it, so this is something which needs +to be handled by platform and generic code, not individual drivers. + + + +8. Vendor and device identifications +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +One is not not required to add new device ids to include/linux/pci_ids.h. +Please add PCI_VENDOR_ID_xxx for vendors and a hex constant for device ids. + +PCI_VENDOR_ID_xxx constants are re-used. The device ids are arbitrary +hex numbers (vendor controlled) and normally used only in a single +location, the pci_device_id table. + +Please DO submit new vendor/device ids to pciids.sourceforge.net project. + + + +9. Obsolete functions +~~~~~~~~~~~~~~~~~~~~~ + +There are several functions which you might come across when trying to +port an old driver to the new PCI interface. They are no longer present +in the kernel as they aren't compatible with hotplug or PCI domains or +having sane locking. + +pci_find_device() Superseded by pci_get_device() +pci_find_subsys() Superseded by pci_get_subsys() +pci_find_slot() Superseded by pci_get_slot() + + +The alternative is the traditional PCI device driver that walks PCI +device lists. This is still possible but discouraged. + + + +10. MMIO Space and "Write Posting" +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +Converting a driver from using I/O Port space to using MMIO space +often requires some additional changes. Specifically, "write posting" +needs to be handled. Many drivers (e.g. tg3, acenic, sym53c8xx_2) +already do this. I/O Port space guarantees write transactions reach the PCI +device before the CPU can continue. Writes to MMIO space allow the CPU +to continue before the transaction reaches the PCI device. HW weenies +call this "Write Posting" because the write completion is "posted" to +the CPU before the transaction has reached its destination. + +Thus, timing sensitive code should add readl() where the CPU is +expected to wait before doing other work. The classic "bit banging" +sequence works fine for I/O Port space: + + for (i = 8; --i; val >>= 1) { + outb(val & 1, ioport_reg); /* write bit */ + udelay(10); + } + +The same sequence for MMIO space should be: + + for (i = 8; --i; val >>= 1) { + writeb(val & 1, mmio_reg); /* write bit */ + readb(safe_mmio_reg); /* flush posted write */ + udelay(10); + } + +It is important that "safe_mmio_reg" not have any side effects that +interferes with the correct operation of the device. + +Another case to watch out for is when resetting a PCI device. Use PCI +Configuration space reads to flush the writel(). This will gracefully +handle the PCI master abort on all platforms if the PCI device is +expected to not respond to a readl(). Most x86 platforms will allow +MMIO reads to master abort (a.k.a. "Soft Fail") and return garbage +(e.g. ~0). But many RISC platforms will crash (a.k.a."Hard Fail"). + diff --git a/Documentation/PCI/pcieaer-howto.txt b/Documentation/PCI/pcieaer-howto.txt new file mode 100644 index 00000000000..be21001ab14 --- /dev/null +++ b/Documentation/PCI/pcieaer-howto.txt @@ -0,0 +1,273 @@ + The PCI Express Advanced Error Reporting Driver Guide HOWTO + T. Long Nguyen <tom.l.nguyen@intel.com> + Yanmin Zhang <yanmin.zhang@intel.com> + 07/29/2006 + + +1. Overview + +1.1 About this guide + +This guide describes the basics of the PCI Express Advanced Error +Reporting (AER) driver and provides information on how to use it, as +well as how to enable the drivers of endpoint devices to conform with +PCI Express AER driver. + +1.2 Copyright © Intel Corporation 2006. + +1.3 What is the PCI Express AER Driver? + +PCI Express error signaling can occur on the PCI Express link itself +or on behalf of transactions initiated on the link. PCI Express +defines two error reporting paradigms: the baseline capability and +the Advanced Error Reporting capability. The baseline capability is +required of all PCI Express components providing a minimum defined +set of error reporting requirements. Advanced Error Reporting +capability is implemented with a PCI Express advanced error reporting +extended capability structure providing more robust error reporting. + +The PCI Express AER driver provides the infrastructure to support PCI +Express Advanced Error Reporting capability. The PCI Express AER +driver provides three basic functions: + +- Gathers the comprehensive error information if errors occurred. +- Reports error to the users. +- Performs error recovery actions. + +AER driver only attaches root ports which support PCI-Express AER +capability. + + +2. User Guide + +2.1 Include the PCI Express AER Root Driver into the Linux Kernel + +The PCI Express AER Root driver is a Root Port service driver attached +to the PCI Express Port Bus driver. If a user wants to use it, the driver +has to be compiled. Option CONFIG_PCIEAER supports this capability. It +depends on CONFIG_PCIEPORTBUS, so pls. set CONFIG_PCIEPORTBUS=y and +CONFIG_PCIEAER = y. + +2.2 Load PCI Express AER Root Driver +There is a case where a system has AER support in BIOS. Enabling the AER +Root driver and having AER support in BIOS may result unpredictable +behavior. To avoid this conflict, a successful load of the AER Root driver +requires ACPI _OSC support in the BIOS to allow the AER Root driver to +request for native control of AER. See the PCI FW 3.0 Specification for +details regarding OSC usage. Currently, lots of firmwares don't provide +_OSC support while they use PCI Express. To support such firmwares, +forceload, a parameter of type bool, could enable AER to continue to +be initiated although firmwares have no _OSC support. To enable the +walkaround, pls. add aerdriver.forceload=y to kernel boot parameter line +when booting kernel. Note that forceload=n by default. + +nosourceid, another parameter of type bool, can be used when broken +hardware (mostly chipsets) has root ports that cannot obtain the reporting +source ID. nosourceid=n by default. + +2.3 AER error output +When a PCI-E AER error is captured, an error message will be outputed to +console. If it's a correctable error, it is outputed as a warning. +Otherwise, it is printed as an error. So users could choose different +log level to filter out correctable error messages. + +Below shows an example. ++------ PCI-Express Device Error -----+ +Error Severity : Uncorrected (Fatal) +PCIE Bus Error type : Transaction Layer +Unsupported Request : First +Requester ID : 0500 +VendorID=8086h, DeviceID=0329h, Bus=05h, Device=00h, Function=00h +TLB Header: +04000001 00200a03 05010000 00050100 + +In the example, 'Requester ID' means the ID of the device who sends +the error message to root port. Pls. refer to pci express specs for +other fields. + + +3. Developer Guide + +To enable AER aware support requires a software driver to configure +the AER capability structure within its device and to provide callbacks. + +To support AER better, developers need understand how AER does work +firstly. + +PCI Express errors are classified into two types: correctable errors +and uncorrectable errors. This classification is based on the impacts +of those errors, which may result in degraded performance or function +failure. + +Correctable errors pose no impacts on the functionality of the +interface. The PCI Express protocol can recover without any software +intervention or any loss of data. These errors are detected and +corrected by hardware. Unlike correctable errors, uncorrectable +errors impact functionality of the interface. Uncorrectable errors +can cause a particular transaction or a particular PCI Express link +to be unreliable. Depending on those error conditions, uncorrectable +errors are further classified into non-fatal errors and fatal errors. +Non-fatal errors cause the particular transaction to be unreliable, +but the PCI Express link itself is fully functional. Fatal errors, on +the other hand, cause the link to be unreliable. + +When AER is enabled, a PCI Express device will automatically send an +error message to the PCIE root port above it when the device captures +an error. The Root Port, upon receiving an error reporting message, +internally processes and logs the error message in its PCI Express +capability structure. Error information being logged includes storing +the error reporting agent's requestor ID into the Error Source +Identification Registers and setting the error bits of the Root Error +Status Register accordingly. If AER error reporting is enabled in Root +Error Command Register, the Root Port generates an interrupt if an +error is detected. + +Note that the errors as described above are related to the PCI Express +hierarchy and links. These errors do not include any device specific +errors because device specific errors will still get sent directly to +the device driver. + +3.1 Configure the AER capability structure + +AER aware drivers of PCI Express component need change the device +control registers to enable AER. They also could change AER registers, +including mask and severity registers. Helper function +pci_enable_pcie_error_reporting could be used to enable AER. See +section 3.3. + +3.2. Provide callbacks + +3.2.1 callback reset_link to reset pci express link + +This callback is used to reset the pci express physical link when a +fatal error happens. The root port aer service driver provides a +default reset_link function, but different upstream ports might +have different specifications to reset pci express link, so all +upstream ports should provide their own reset_link functions. + +In struct pcie_port_service_driver, a new pointer, reset_link, is +added. + +pci_ers_result_t (*reset_link) (struct pci_dev *dev); + +Section 3.2.2.2 provides more detailed info on when to call +reset_link. + +3.2.2 PCI error-recovery callbacks + +The PCI Express AER Root driver uses error callbacks to coordinate +with downstream device drivers associated with a hierarchy in question +when performing error recovery actions. + +Data struct pci_driver has a pointer, err_handler, to point to +pci_error_handlers who consists of a couple of callback function +pointers. AER driver follows the rules defined in +pci-error-recovery.txt except pci express specific parts (e.g. +reset_link). Pls. refer to pci-error-recovery.txt for detailed +definitions of the callbacks. + +Below sections specify when to call the error callback functions. + +3.2.2.1 Correctable errors + +Correctable errors pose no impacts on the functionality of +the interface. The PCI Express protocol can recover without any +software intervention or any loss of data. These errors do not +require any recovery actions. The AER driver clears the device's +correctable error status register accordingly and logs these errors. + +3.2.2.2 Non-correctable (non-fatal and fatal) errors + +If an error message indicates a non-fatal error, performing link reset +at upstream is not required. The AER driver calls error_detected(dev, +pci_channel_io_normal) to all drivers associated within a hierarchy in +question. for example, +EndPoint<==>DownstreamPort B<==>UpstreamPort A<==>RootPort. +If Upstream port A captures an AER error, the hierarchy consists of +Downstream port B and EndPoint. + +A driver may return PCI_ERS_RESULT_CAN_RECOVER, +PCI_ERS_RESULT_DISCONNECT, or PCI_ERS_RESULT_NEED_RESET, depending on +whether it can recover or the AER driver calls mmio_enabled as next. + +If an error message indicates a fatal error, kernel will broadcast +error_detected(dev, pci_channel_io_frozen) to all drivers within +a hierarchy in question. Then, performing link reset at upstream is +necessary. As different kinds of devices might use different approaches +to reset link, AER port service driver is required to provide the +function to reset link. Firstly, kernel looks for if the upstream +component has an aer driver. If it has, kernel uses the reset_link +callback of the aer driver. If the upstream component has no aer driver +and the port is downstream port, we will use the aer driver of the +root port who reports the AER error. As for upstream ports, +they should provide their own aer service drivers with reset_link +function. If error_detected returns PCI_ERS_RESULT_CAN_RECOVER and +reset_link returns PCI_ERS_RESULT_RECOVERED, the error handling goes +to mmio_enabled. + +3.3 helper functions + +3.3.1 int pci_enable_pcie_error_reporting(struct pci_dev *dev); +pci_enable_pcie_error_reporting enables the device to send error +messages to root port when an error is detected. Note that devices +don't enable the error reporting by default, so device drivers need +call this function to enable it. + +3.3.2 int pci_disable_pcie_error_reporting(struct pci_dev *dev); +pci_disable_pcie_error_reporting disables the device to send error +messages to root port when an error is detected. + +3.3.3 int pci_cleanup_aer_uncorrect_error_status(struct pci_dev *dev); +pci_cleanup_aer_uncorrect_error_status cleanups the uncorrectable +error status register. + +3.4 Frequent Asked Questions + +Q: What happens if a PCI Express device driver does not provide an +error recovery handler (pci_driver->err_handler is equal to NULL)? + +A: The devices attached with the driver won't be recovered. If the +error is fatal, kernel will print out warning messages. Please refer +to section 3 for more information. + +Q: What happens if an upstream port service driver does not provide +callback reset_link? + +A: Fatal error recovery will fail if the errors are reported by the +upstream ports who are attached by the service driver. + +Q: How does this infrastructure deal with driver that is not PCI +Express aware? + +A: This infrastructure calls the error callback functions of the +driver when an error happens. But if the driver is not aware of +PCI Express, the device might not report its own errors to root +port. + +Q: What modifications will that driver need to make it compatible +with the PCI Express AER Root driver? + +A: It could call the helper functions to enable AER in devices and +cleanup uncorrectable status register. Pls. refer to section 3.3. + + +4. Software error injection + +Debugging PCIE AER error recovery code is quite difficult because it +is hard to trigger real hardware errors. Software based error +injection can be used to fake various kinds of PCIE errors. + +First you should enable PCIE AER software error injection in kernel +configuration, that is, following item should be in your .config. + +CONFIG_PCIEAER_INJECT=y or CONFIG_PCIEAER_INJECT=m + +After reboot with new kernel or insert the module, a device file named +/dev/aer_inject should be created. + +Then, you need a user space tool named aer-inject, which can be gotten +from: + http://www.kernel.org/pub/linux/utils/pci/aer-inject/ + +More information about aer-inject can be found in the document comes +with its source code. |