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-EISA bus support (Marc Zyngier <maz@wild-wind.fr.eu.org>)
-
-This document groups random notes about porting EISA drivers to the
-new EISA/sysfs API.
-
-Starting from version 2.5.59, the EISA bus is almost given the same
-status as other much more mainstream busses such as PCI or USB. This
-has been possible through sysfs, which defines a nice enough set of
-abstractions to manage busses, devices and drivers.
-
-Although the new API is quite simple to use, converting existing
-drivers to the new infrastructure is not an easy task (mostly because
-detection code is generally also used to probe ISA cards). Moreover,
-most EISA drivers are among the oldest Linux drivers so, as you can
-imagine, some dust has settled here over the years.
-
-The EISA infrastructure is made up of three parts :
-
- - The bus code implements most of the generic code. It is shared
- among all the architectures that the EISA code runs on. It
- implements bus probing (detecting EISA cards available on the bus),
- allocates I/O resources, allows fancy naming through sysfs, and
- offers interfaces for driver to register.
-
- - The bus root driver implements the glue between the bus hardware
- and the generic bus code. It is responsible for discovering the
- device implementing the bus, and setting it up to be latter probed
- by the bus code. This can go from something as simple as reserving
- an I/O region on x86, to the rather more complex, like the hppa
- EISA code. This is the part to implement in order to have EISA
- running on an "new" platform.
-
- - The driver offers the bus a list of devices that it manages, and
- implements the necessary callbacks to probe and release devices
- whenever told to.
-
-Every function/structure below lives in <linux/eisa.h>, which depends
-heavily on <linux/device.h>.
-
-** Bus root driver :
-
-int eisa_root_register (struct eisa_root_device *root);
-
-The eisa_root_register function is used to declare a device as the
-root of an EISA bus. The eisa_root_device structure holds a reference
-to this device, as well as some parameters for probing purposes.
-
-struct eisa_root_device {
- struct device *dev; /* Pointer to bridge device */
- struct resource *res;
- unsigned long bus_base_addr;
- int slots; /* Max slot number */
- int force_probe; /* Probe even when no slot 0 */
- u64 dma_mask; /* from bridge device */
- int bus_nr; /* Set by eisa_root_register */
- struct resource eisa_root_res; /* ditto */
-};
-
-node : used for eisa_root_register internal purpose
-dev : pointer to the root device
-res : root device I/O resource
-bus_base_addr : slot 0 address on this bus
-slots : max slot number to probe
-force_probe : Probe even when slot 0 is empty (no EISA mainboard)
-dma_mask : Default DMA mask. Usually the bridge device dma_mask.
-bus_nr : unique bus id, set by eisa_root_register
-
-** Driver :
-
-int eisa_driver_register (struct eisa_driver *edrv);
-void eisa_driver_unregister (struct eisa_driver *edrv);
-
-Clear enough ?
-
-struct eisa_device_id {
- char sig[EISA_SIG_LEN];
- unsigned long driver_data;
-};
-
-struct eisa_driver {
- const struct eisa_device_id *id_table;
- struct device_driver driver;
-};
-
-id_table : an array of NULL terminated EISA id strings,
- followed by an empty string. Each string can
- optionally be paired with a driver-dependent value
- (driver_data).
-
-driver : a generic driver, such as described in
- Documentation/driver-model/driver.txt. Only .name,
- .probe and .remove members are mandatory.
-
-An example is the 3c59x driver :
-
-static struct eisa_device_id vortex_eisa_ids[] = {
- { "TCM5920", EISA_3C592_OFFSET },
- { "TCM5970", EISA_3C597_OFFSET },
- { "" }
-};
-
-static struct eisa_driver vortex_eisa_driver = {
- .id_table = vortex_eisa_ids,
- .driver = {
- .name = "3c59x",
- .probe = vortex_eisa_probe,
- .remove = vortex_eisa_remove
- }
-};
-
-** Device :
-
-The sysfs framework calls .probe and .remove functions upon device
-discovery and removal (note that the .remove function is only called
-when driver is built as a module).
-
-Both functions are passed a pointer to a 'struct device', which is
-encapsulated in a 'struct eisa_device' described as follows :
-
-struct eisa_device {
- struct eisa_device_id id;
- int slot;
- int state;
- unsigned long base_addr;
- struct resource res[EISA_MAX_RESOURCES];
- u64 dma_mask;
- struct device dev; /* generic device */
-};
-
-id : EISA id, as read from device. id.driver_data is set from the
- matching driver EISA id.
-slot : slot number which the device was detected on
-state : set of flags indicating the state of the device. Current
- flags are EISA_CONFIG_ENABLED and EISA_CONFIG_FORCED.
-res : set of four 256 bytes I/O regions allocated to this device
-dma_mask: DMA mask set from the parent device.
-dev : generic device (see Documentation/driver-model/device.txt)
-
-You can get the 'struct eisa_device' from 'struct device' using the
-'to_eisa_device' macro.
-
-** Misc stuff :
-
-void eisa_set_drvdata (struct eisa_device *edev, void *data);
-
-Stores data into the device's driver_data area.
-
-void *eisa_get_drvdata (struct eisa_device *edev):
-
-Gets the pointer previously stored into the device's driver_data area.
-
-int eisa_get_region_index (void *addr);
-
-Returns the region number (0 <= x < EISA_MAX_RESOURCES) of a given
-address.
-
-** Kernel parameters :
-
-eisa_bus.enable_dev :
-
-A comma-separated list of slots to be enabled, even if the firmware
-set the card as disabled. The driver must be able to properly
-initialize the device in such conditions.
-
-eisa_bus.disable_dev :
-
-A comma-separated list of slots to be enabled, even if the firmware
-set the card as enabled. The driver won't be called to handle this
-device.
-
-virtual_root.force_probe :
-
-Force the probing code to probe EISA slots even when it cannot find an
-EISA compliant mainboard (nothing appears on slot 0). Defaults to 0
-(don't force), and set to 1 (force probing) when either
-CONFIG_ALPHA_JENSEN or CONFIG_EISA_VLB_PRIMING are set.
-
-** Random notes :
-
-Converting an EISA driver to the new API mostly involves *deleting*
-code (since probing is now in the core EISA code). Unfortunately, most
-drivers share their probing routine between ISA, and EISA. Special
-care must be taken when ripping out the EISA code, so other busses
-won't suffer from these surgical strikes...
-
-You *must not* expect any EISA device to be detected when returning
-from eisa_driver_register, since the chances are that the bus has not
-yet been probed. In fact, that's what happens most of the time (the
-bus root driver usually kicks in rather late in the boot process).
-Unfortunately, most drivers are doing the probing by themselves, and
-expect to have explored the whole machine when they exit their probe
-routine.
-
-For example, switching your favorite EISA SCSI card to the "hotplug"
-model is "the right thing"(tm).
-
-** Thanks :
-
-I'd like to thank the following people for their help :
-- Xavier Benigni for lending me a wonderful Alpha Jensen,
-- James Bottomley, Jeff Garzik for getting this stuff into the kernel,
-- Andries Brouwer for contributing numerous EISA ids,
-- Catrin Jones for coping with far too many machines at home.