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-<?xml version="1.0" encoding="UTF-8"?>
-<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
-"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd" []>
-
-<book id="index">
-<bookinfo>
-<title>The Userspace I/O HOWTO</title>
-
-<author>
- <firstname>Hans-Jürgen</firstname>
- <surname>Koch</surname>
- <authorblurb><para>Linux developer, Linutronix</para></authorblurb>
- <affiliation>
- <orgname>
- <ulink url="http://www.linutronix.de">Linutronix</ulink>
- </orgname>
-
- <address>
- <email>hjk@hansjkoch.de</email>
- </address>
- </affiliation>
-</author>
-
-<copyright>
- <year>2006-2008</year>
- <holder>Hans-Jürgen Koch.</holder>
-</copyright>
-<copyright>
- <year>2009</year>
- <holder>Red Hat Inc, Michael S. Tsirkin (mst@redhat.com)</holder>
-</copyright>
-
-<legalnotice>
-<para>
-This documentation is Free Software licensed under the terms of the
-GPL version 2.
-</para>
-</legalnotice>
-
-<pubdate>2006-12-11</pubdate>
-
-<abstract>
- <para>This HOWTO describes concept and usage of Linux kernel's
- Userspace I/O system.</para>
-</abstract>
-
-<revhistory>
- <revision>
- <revnumber>0.9</revnumber>
- <date>2009-07-16</date>
- <authorinitials>mst</authorinitials>
- <revremark>Added generic pci driver
- </revremark>
- </revision>
- <revision>
- <revnumber>0.8</revnumber>
- <date>2008-12-24</date>
- <authorinitials>hjk</authorinitials>
- <revremark>Added name attributes in mem and portio sysfs directories.
- </revremark>
- </revision>
- <revision>
- <revnumber>0.7</revnumber>
- <date>2008-12-23</date>
- <authorinitials>hjk</authorinitials>
- <revremark>Added generic platform drivers and offset attribute.</revremark>
- </revision>
- <revision>
- <revnumber>0.6</revnumber>
- <date>2008-12-05</date>
- <authorinitials>hjk</authorinitials>
- <revremark>Added description of portio sysfs attributes.</revremark>
- </revision>
- <revision>
- <revnumber>0.5</revnumber>
- <date>2008-05-22</date>
- <authorinitials>hjk</authorinitials>
- <revremark>Added description of write() function.</revremark>
- </revision>
- <revision>
- <revnumber>0.4</revnumber>
- <date>2007-11-26</date>
- <authorinitials>hjk</authorinitials>
- <revremark>Removed section about uio_dummy.</revremark>
- </revision>
- <revision>
- <revnumber>0.3</revnumber>
- <date>2007-04-29</date>
- <authorinitials>hjk</authorinitials>
- <revremark>Added section about userspace drivers.</revremark>
- </revision>
- <revision>
- <revnumber>0.2</revnumber>
- <date>2007-02-13</date>
- <authorinitials>hjk</authorinitials>
- <revremark>Update after multiple mappings were added.</revremark>
- </revision>
- <revision>
- <revnumber>0.1</revnumber>
- <date>2006-12-11</date>
- <authorinitials>hjk</authorinitials>
- <revremark>First draft.</revremark>
- </revision>
-</revhistory>
-</bookinfo>
-
-<chapter id="aboutthisdoc">
-<?dbhtml filename="aboutthis.html"?>
-<title>About this document</title>
-
-<sect1 id="translations">
-<?dbhtml filename="translations.html"?>
-<title>Translations</title>
-
-<para>If you know of any translations for this document, or you are
-interested in translating it, please email me
-<email>hjk@hansjkoch.de</email>.
-</para>
-</sect1>
-
-<sect1 id="preface">
-<title>Preface</title>
- <para>
- For many types of devices, creating a Linux kernel driver is
- overkill. All that is really needed is some way to handle an
- interrupt and provide access to the memory space of the
- device. The logic of controlling the device does not
- necessarily have to be within the kernel, as the device does
- not need to take advantage of any of other resources that the
- kernel provides. One such common class of devices that are
- like this are for industrial I/O cards.
- </para>
- <para>
- To address this situation, the userspace I/O system (UIO) was
- designed. For typical industrial I/O cards, only a very small
- kernel module is needed. The main part of the driver will run in
- user space. This simplifies development and reduces the risk of
- serious bugs within a kernel module.
- </para>
- <para>
- Please note that UIO is not an universal driver interface. Devices
- that are already handled well by other kernel subsystems (like
- networking or serial or USB) are no candidates for an UIO driver.
- Hardware that is ideally suited for an UIO driver fulfills all of
- the following:
- </para>
-<itemizedlist>
-<listitem>
- <para>The device has memory that can be mapped. The device can be
- controlled completely by writing to this memory.</para>
-</listitem>
-<listitem>
- <para>The device usually generates interrupts.</para>
-</listitem>
-<listitem>
- <para>The device does not fit into one of the standard kernel
- subsystems.</para>
-</listitem>
-</itemizedlist>
-</sect1>
-
-<sect1 id="thanks">
-<title>Acknowledgments</title>
- <para>I'd like to thank Thomas Gleixner and Benedikt Spranger of
- Linutronix, who have not only written most of the UIO code, but also
- helped greatly writing this HOWTO by giving me all kinds of background
- information.</para>
-</sect1>
-
-<sect1 id="feedback">
-<title>Feedback</title>
- <para>Find something wrong with this document? (Or perhaps something
- right?) I would love to hear from you. Please email me at
- <email>hjk@hansjkoch.de</email>.</para>
-</sect1>
-</chapter>
-
-<chapter id="about">
-<?dbhtml filename="about.html"?>
-<title>About UIO</title>
-
-<para>If you use UIO for your card's driver, here's what you get:</para>
-
-<itemizedlist>
-<listitem>
- <para>only one small kernel module to write and maintain.</para>
-</listitem>
-<listitem>
- <para>develop the main part of your driver in user space,
- with all the tools and libraries you're used to.</para>
-</listitem>
-<listitem>
- <para>bugs in your driver won't crash the kernel.</para>
-</listitem>
-<listitem>
- <para>updates of your driver can take place without recompiling
- the kernel.</para>
-</listitem>
-</itemizedlist>
-
-<sect1 id="how_uio_works">
-<title>How UIO works</title>
- <para>
- Each UIO device is accessed through a device file and several
- sysfs attribute files. The device file will be called
- <filename>/dev/uio0</filename> for the first device, and
- <filename>/dev/uio1</filename>, <filename>/dev/uio2</filename>
- and so on for subsequent devices.
- </para>
-
- <para><filename>/dev/uioX</filename> is used to access the
- address space of the card. Just use
- <function>mmap()</function> to access registers or RAM
- locations of your card.
- </para>
-
- <para>
- Interrupts are handled by reading from
- <filename>/dev/uioX</filename>. A blocking
- <function>read()</function> from
- <filename>/dev/uioX</filename> will return as soon as an
- interrupt occurs. You can also use
- <function>select()</function> on
- <filename>/dev/uioX</filename> to wait for an interrupt. The
- integer value read from <filename>/dev/uioX</filename>
- represents the total interrupt count. You can use this number
- to figure out if you missed some interrupts.
- </para>
- <para>
- For some hardware that has more than one interrupt source internally,
- but not separate IRQ mask and status registers, there might be
- situations where userspace cannot determine what the interrupt source
- was if the kernel handler disables them by writing to the chip's IRQ
- register. In such a case, the kernel has to disable the IRQ completely
- to leave the chip's register untouched. Now the userspace part can
- determine the cause of the interrupt, but it cannot re-enable
- interrupts. Another cornercase is chips where re-enabling interrupts
- is a read-modify-write operation to a combined IRQ status/acknowledge
- register. This would be racy if a new interrupt occurred
- simultaneously.
- </para>
- <para>
- To address these problems, UIO also implements a write() function. It
- is normally not used and can be ignored for hardware that has only a
- single interrupt source or has separate IRQ mask and status registers.
- If you need it, however, a write to <filename>/dev/uioX</filename>
- will call the <function>irqcontrol()</function> function implemented
- by the driver. You have to write a 32-bit value that is usually either
- 0 or 1 to disable or enable interrupts. If a driver does not implement
- <function>irqcontrol()</function>, <function>write()</function> will
- return with <varname>-ENOSYS</varname>.
- </para>
-
- <para>
- To handle interrupts properly, your custom kernel module can
- provide its own interrupt handler. It will automatically be
- called by the built-in handler.
- </para>
-
- <para>
- For cards that don't generate interrupts but need to be
- polled, there is the possibility to set up a timer that
- triggers the interrupt handler at configurable time intervals.
- This interrupt simulation is done by calling
- <function>uio_event_notify()</function>
- from the timer's event handler.
- </para>
-
- <para>
- Each driver provides attributes that are used to read or write
- variables. These attributes are accessible through sysfs
- files. A custom kernel driver module can add its own
- attributes to the device owned by the uio driver, but not added
- to the UIO device itself at this time. This might change in the
- future if it would be found to be useful.
- </para>
-
- <para>
- The following standard attributes are provided by the UIO
- framework:
- </para>
-<itemizedlist>
-<listitem>
- <para>
- <filename>name</filename>: The name of your device. It is
- recommended to use the name of your kernel module for this.
- </para>
-</listitem>
-<listitem>
- <para>
- <filename>version</filename>: A version string defined by your
- driver. This allows the user space part of your driver to deal
- with different versions of the kernel module.
- </para>
-</listitem>
-<listitem>
- <para>
- <filename>event</filename>: The total number of interrupts
- handled by the driver since the last time the device node was
- read.
- </para>
-</listitem>
-</itemizedlist>
-<para>
- These attributes appear under the
- <filename>/sys/class/uio/uioX</filename> directory. Please
- note that this directory might be a symlink, and not a real
- directory. Any userspace code that accesses it must be able
- to handle this.
-</para>
-<para>
- Each UIO device can make one or more memory regions available for
- memory mapping. This is necessary because some industrial I/O cards
- require access to more than one PCI memory region in a driver.
-</para>
-<para>
- Each mapping has its own directory in sysfs, the first mapping
- appears as <filename>/sys/class/uio/uioX/maps/map0/</filename>.
- Subsequent mappings create directories <filename>map1/</filename>,
- <filename>map2/</filename>, and so on. These directories will only
- appear if the size of the mapping is not 0.
-</para>
-<para>
- Each <filename>mapX/</filename> directory contains four read-only files
- that show attributes of the memory:
-</para>
-<itemizedlist>
-<listitem>
- <para>
- <filename>name</filename>: A string identifier for this mapping. This
- is optional, the string can be empty. Drivers can set this to make it
- easier for userspace to find the correct mapping.
- </para>
-</listitem>
-<listitem>
- <para>
- <filename>addr</filename>: The address of memory that can be mapped.
- </para>
-</listitem>
-<listitem>
- <para>
- <filename>size</filename>: The size, in bytes, of the memory
- pointed to by addr.
- </para>
-</listitem>
-<listitem>
- <para>
- <filename>offset</filename>: The offset, in bytes, that has to be
- added to the pointer returned by <function>mmap()</function> to get
- to the actual device memory. This is important if the device's memory
- is not page aligned. Remember that pointers returned by
- <function>mmap()</function> are always page aligned, so it is good
- style to always add this offset.
- </para>
-</listitem>
-</itemizedlist>
-
-<para>
- From userspace, the different mappings are distinguished by adjusting
- the <varname>offset</varname> parameter of the
- <function>mmap()</function> call. To map the memory of mapping N, you
- have to use N times the page size as your offset:
-</para>
-<programlisting format="linespecific">
-offset = N * getpagesize();
-</programlisting>
-
-<para>
- Sometimes there is hardware with memory-like regions that can not be
- mapped with the technique described here, but there are still ways to
- access them from userspace. The most common example are x86 ioports.
- On x86 systems, userspace can access these ioports using
- <function>ioperm()</function>, <function>iopl()</function>,
- <function>inb()</function>, <function>outb()</function>, and similar
- functions.
-</para>
-<para>
- Since these ioport regions can not be mapped, they will not appear under
- <filename>/sys/class/uio/uioX/maps/</filename> like the normal memory
- described above. Without information about the port regions a hardware
- has to offer, it becomes difficult for the userspace part of the
- driver to find out which ports belong to which UIO device.
-</para>
-<para>
- To address this situation, the new directory
- <filename>/sys/class/uio/uioX/portio/</filename> was added. It only
- exists if the driver wants to pass information about one or more port
- regions to userspace. If that is the case, subdirectories named
- <filename>port0</filename>, <filename>port1</filename>, and so on,
- will appear underneath
- <filename>/sys/class/uio/uioX/portio/</filename>.
-</para>
-<para>
- Each <filename>portX/</filename> directory contains four read-only
- files that show name, start, size, and type of the port region:
-</para>
-<itemizedlist>
-<listitem>
- <para>
- <filename>name</filename>: A string identifier for this port region.
- The string is optional and can be empty. Drivers can set it to make it
- easier for userspace to find a certain port region.
- </para>
-</listitem>
-<listitem>
- <para>
- <filename>start</filename>: The first port of this region.
- </para>
-</listitem>
-<listitem>
- <para>
- <filename>size</filename>: The number of ports in this region.
- </para>
-</listitem>
-<listitem>
- <para>
- <filename>porttype</filename>: A string describing the type of port.
- </para>
-</listitem>
-</itemizedlist>
-
-
-</sect1>
-</chapter>
-
-<chapter id="custom_kernel_module" xreflabel="Writing your own kernel module">
-<?dbhtml filename="custom_kernel_module.html"?>
-<title>Writing your own kernel module</title>
- <para>
- Please have a look at <filename>uio_cif.c</filename> as an
- example. The following paragraphs explain the different
- sections of this file.
- </para>
-
-<sect1 id="uio_info">
-<title>struct uio_info</title>
- <para>
- This structure tells the framework the details of your driver,
- Some of the members are required, others are optional.
- </para>
-
-<itemizedlist>
-<listitem><para>
-<varname>const char *name</varname>: Required. The name of your driver as
-it will appear in sysfs. I recommend using the name of your module for this.
-</para></listitem>
-
-<listitem><para>
-<varname>const char *version</varname>: Required. This string appears in
-<filename>/sys/class/uio/uioX/version</filename>.
-</para></listitem>
-
-<listitem><para>
-<varname>struct uio_mem mem[ MAX_UIO_MAPS ]</varname>: Required if you
-have memory that can be mapped with <function>mmap()</function>. For each
-mapping you need to fill one of the <varname>uio_mem</varname> structures.
-See the description below for details.
-</para></listitem>
-
-<listitem><para>
-<varname>struct uio_port port[ MAX_UIO_PORTS_REGIONS ]</varname>: Required
-if you want to pass information about ioports to userspace. For each port
-region you need to fill one of the <varname>uio_port</varname> structures.
-See the description below for details.
-</para></listitem>
-
-<listitem><para>
-<varname>long irq</varname>: Required. If your hardware generates an
-interrupt, it's your modules task to determine the irq number during
-initialization. If you don't have a hardware generated interrupt but
-want to trigger the interrupt handler in some other way, set
-<varname>irq</varname> to <varname>UIO_IRQ_CUSTOM</varname>.
-If you had no interrupt at all, you could set
-<varname>irq</varname> to <varname>UIO_IRQ_NONE</varname>, though this
-rarely makes sense.
-</para></listitem>
-
-<listitem><para>
-<varname>unsigned long irq_flags</varname>: Required if you've set
-<varname>irq</varname> to a hardware interrupt number. The flags given
-here will be used in the call to <function>request_irq()</function>.
-</para></listitem>
-
-<listitem><para>
-<varname>int (*mmap)(struct uio_info *info, struct vm_area_struct
-*vma)</varname>: Optional. If you need a special
-<function>mmap()</function> function, you can set it here. If this
-pointer is not NULL, your <function>mmap()</function> will be called
-instead of the built-in one.
-</para></listitem>
-
-<listitem><para>
-<varname>int (*open)(struct uio_info *info, struct inode *inode)
-</varname>: Optional. You might want to have your own
-<function>open()</function>, e.g. to enable interrupts only when your
-device is actually used.
-</para></listitem>
-
-<listitem><para>
-<varname>int (*release)(struct uio_info *info, struct inode *inode)
-</varname>: Optional. If you define your own
-<function>open()</function>, you will probably also want a custom
-<function>release()</function> function.
-</para></listitem>
-
-<listitem><para>
-<varname>int (*irqcontrol)(struct uio_info *info, s32 irq_on)
-</varname>: Optional. If you need to be able to enable or disable
-interrupts from userspace by writing to <filename>/dev/uioX</filename>,
-you can implement this function. The parameter <varname>irq_on</varname>
-will be 0 to disable interrupts and 1 to enable them.
-</para></listitem>
-</itemizedlist>
-
-<para>
-Usually, your device will have one or more memory regions that can be mapped
-to user space. For each region, you have to set up a
-<varname>struct uio_mem</varname> in the <varname>mem[]</varname> array.
-Here's a description of the fields of <varname>struct uio_mem</varname>:
-</para>
-
-<itemizedlist>
-<listitem><para>
-<varname>const char *name</varname>: Optional. Set this to help identify
-the memory region, it will show up in the corresponding sysfs node.
-</para></listitem>
-
-<listitem><para>
-<varname>int memtype</varname>: Required if the mapping is used. Set this to
-<varname>UIO_MEM_PHYS</varname> if you you have physical memory on your
-card to be mapped. Use <varname>UIO_MEM_LOGICAL</varname> for logical
-memory (e.g. allocated with <function>kmalloc()</function>). There's also
-<varname>UIO_MEM_VIRTUAL</varname> for virtual memory.
-</para></listitem>
-
-<listitem><para>
-<varname>phys_addr_t addr</varname>: Required if the mapping is used.
-Fill in the address of your memory block. This address is the one that
-appears in sysfs.
-</para></listitem>
-
-<listitem><para>
-<varname>unsigned long size</varname>: Fill in the size of the
-memory block that <varname>addr</varname> points to. If <varname>size</varname>
-is zero, the mapping is considered unused. Note that you
-<emphasis>must</emphasis> initialize <varname>size</varname> with zero for
-all unused mappings.
-</para></listitem>
-
-<listitem><para>
-<varname>void *internal_addr</varname>: If you have to access this memory
-region from within your kernel module, you will want to map it internally by
-using something like <function>ioremap()</function>. Addresses
-returned by this function cannot be mapped to user space, so you must not
-store it in <varname>addr</varname>. Use <varname>internal_addr</varname>
-instead to remember such an address.
-</para></listitem>
-</itemizedlist>
-
-<para>
-Please do not touch the <varname>map</varname> element of
-<varname>struct uio_mem</varname>! It is used by the UIO framework
-to set up sysfs files for this mapping. Simply leave it alone.
-</para>
-
-<para>
-Sometimes, your device can have one or more port regions which can not be
-mapped to userspace. But if there are other possibilities for userspace to
-access these ports, it makes sense to make information about the ports
-available in sysfs. For each region, you have to set up a
-<varname>struct uio_port</varname> in the <varname>port[]</varname> array.
-Here's a description of the fields of <varname>struct uio_port</varname>:
-</para>
-
-<itemizedlist>
-<listitem><para>
-<varname>char *porttype</varname>: Required. Set this to one of the predefined
-constants. Use <varname>UIO_PORT_X86</varname> for the ioports found in x86
-architectures.
-</para></listitem>
-
-<listitem><para>
-<varname>unsigned long start</varname>: Required if the port region is used.
-Fill in the number of the first port of this region.
-</para></listitem>
-
-<listitem><para>
-<varname>unsigned long size</varname>: Fill in the number of ports in this
-region. If <varname>size</varname> is zero, the region is considered unused.
-Note that you <emphasis>must</emphasis> initialize <varname>size</varname>
-with zero for all unused regions.
-</para></listitem>
-</itemizedlist>
-
-<para>
-Please do not touch the <varname>portio</varname> element of
-<varname>struct uio_port</varname>! It is used internally by the UIO
-framework to set up sysfs files for this region. Simply leave it alone.
-</para>
-
-</sect1>
-
-<sect1 id="adding_irq_handler">
-<title>Adding an interrupt handler</title>
- <para>
- What you need to do in your interrupt handler depends on your
- hardware and on how you want to handle it. You should try to
- keep the amount of code in your kernel interrupt handler low.
- If your hardware requires no action that you
- <emphasis>have</emphasis> to perform after each interrupt,
- then your handler can be empty.</para> <para>If, on the other
- hand, your hardware <emphasis>needs</emphasis> some action to
- be performed after each interrupt, then you
- <emphasis>must</emphasis> do it in your kernel module. Note
- that you cannot rely on the userspace part of your driver. Your
- userspace program can terminate at any time, possibly leaving
- your hardware in a state where proper interrupt handling is
- still required.
- </para>
-
- <para>
- There might also be applications where you want to read data
- from your hardware at each interrupt and buffer it in a piece
- of kernel memory you've allocated for that purpose. With this
- technique you could avoid loss of data if your userspace
- program misses an interrupt.
- </para>
-
- <para>
- A note on shared interrupts: Your driver should support
- interrupt sharing whenever this is possible. It is possible if
- and only if your driver can detect whether your hardware has
- triggered the interrupt or not. This is usually done by looking
- at an interrupt status register. If your driver sees that the
- IRQ bit is actually set, it will perform its actions, and the
- handler returns IRQ_HANDLED. If the driver detects that it was
- not your hardware that caused the interrupt, it will do nothing
- and return IRQ_NONE, allowing the kernel to call the next
- possible interrupt handler.
- </para>
-
- <para>
- If you decide not to support shared interrupts, your card
- won't work in computers with no free interrupts. As this
- frequently happens on the PC platform, you can save yourself a
- lot of trouble by supporting interrupt sharing.
- </para>
-</sect1>
-
-<sect1 id="using_uio_pdrv">
-<title>Using uio_pdrv for platform devices</title>
- <para>
- In many cases, UIO drivers for platform devices can be handled in a
- generic way. In the same place where you define your
- <varname>struct platform_device</varname>, you simply also implement
- your interrupt handler and fill your
- <varname>struct uio_info</varname>. A pointer to this
- <varname>struct uio_info</varname> is then used as
- <varname>platform_data</varname> for your platform device.
- </para>
- <para>
- You also need to set up an array of <varname>struct resource</varname>
- containing addresses and sizes of your memory mappings. This
- information is passed to the driver using the
- <varname>.resource</varname> and <varname>.num_resources</varname>
- elements of <varname>struct platform_device</varname>.
- </para>
- <para>
- You now have to set the <varname>.name</varname> element of
- <varname>struct platform_device</varname> to
- <varname>"uio_pdrv"</varname> to use the generic UIO platform device
- driver. This driver will fill the <varname>mem[]</varname> array
- according to the resources given, and register the device.
- </para>
- <para>
- The advantage of this approach is that you only have to edit a file
- you need to edit anyway. You do not have to create an extra driver.
- </para>
-</sect1>
-
-<sect1 id="using_uio_pdrv_genirq">
-<title>Using uio_pdrv_genirq for platform devices</title>
- <para>
- Especially in embedded devices, you frequently find chips where the
- irq pin is tied to its own dedicated interrupt line. In such cases,
- where you can be really sure the interrupt is not shared, we can take
- the concept of <varname>uio_pdrv</varname> one step further and use a
- generic interrupt handler. That's what
- <varname>uio_pdrv_genirq</varname> does.
- </para>
- <para>
- The setup for this driver is the same as described above for
- <varname>uio_pdrv</varname>, except that you do not implement an
- interrupt handler. The <varname>.handler</varname> element of
- <varname>struct uio_info</varname> must remain
- <varname>NULL</varname>. The <varname>.irq_flags</varname> element
- must not contain <varname>IRQF_SHARED</varname>.
- </para>
- <para>
- You will set the <varname>.name</varname> element of
- <varname>struct platform_device</varname> to
- <varname>"uio_pdrv_genirq"</varname> to use this driver.
- </para>
- <para>
- The generic interrupt handler of <varname>uio_pdrv_genirq</varname>
- will simply disable the interrupt line using
- <function>disable_irq_nosync()</function>. After doing its work,
- userspace can reenable the interrupt by writing 0x00000001 to the UIO
- device file. The driver already implements an
- <function>irq_control()</function> to make this possible, you must not
- implement your own.
- </para>
- <para>
- Using <varname>uio_pdrv_genirq</varname> not only saves a few lines of
- interrupt handler code. You also do not need to know anything about
- the chip's internal registers to create the kernel part of the driver.
- All you need to know is the irq number of the pin the chip is
- connected to.
- </para>
-</sect1>
-
-</chapter>
-
-<chapter id="userspace_driver" xreflabel="Writing a driver in user space">
-<?dbhtml filename="userspace_driver.html"?>
-<title>Writing a driver in userspace</title>
- <para>
- Once you have a working kernel module for your hardware, you can
- write the userspace part of your driver. You don't need any special
- libraries, your driver can be written in any reasonable language,
- you can use floating point numbers and so on. In short, you can
- use all the tools and libraries you'd normally use for writing a
- userspace application.
- </para>
-
-<sect1 id="getting_uio_information">
-<title>Getting information about your UIO device</title>
- <para>
- Information about all UIO devices is available in sysfs. The
- first thing you should do in your driver is check
- <varname>name</varname> and <varname>version</varname> to
- make sure your talking to the right device and that its kernel
- driver has the version you expect.
- </para>
- <para>
- You should also make sure that the memory mapping you need
- exists and has the size you expect.
- </para>
- <para>
- There is a tool called <varname>lsuio</varname> that lists
- UIO devices and their attributes. It is available here:
- </para>
- <para>
- <ulink url="http://www.osadl.org/projects/downloads/UIO/user/">
- http://www.osadl.org/projects/downloads/UIO/user/</ulink>
- </para>
- <para>
- With <varname>lsuio</varname> you can quickly check if your
- kernel module is loaded and which attributes it exports.
- Have a look at the manpage for details.
- </para>
- <para>
- The source code of <varname>lsuio</varname> can serve as an
- example for getting information about an UIO device.
- The file <filename>uio_helper.c</filename> contains a lot of
- functions you could use in your userspace driver code.
- </para>
-</sect1>
-
-<sect1 id="mmap_device_memory">
-<title>mmap() device memory</title>
- <para>
- After you made sure you've got the right device with the
- memory mappings you need, all you have to do is to call
- <function>mmap()</function> to map the device's memory
- to userspace.
- </para>
- <para>
- The parameter <varname>offset</varname> of the
- <function>mmap()</function> call has a special meaning
- for UIO devices: It is used to select which mapping of
- your device you want to map. To map the memory of
- mapping N, you have to use N times the page size as
- your offset:
- </para>
-<programlisting format="linespecific">
- offset = N * getpagesize();
-</programlisting>
- <para>
- N starts from zero, so if you've got only one memory
- range to map, set <varname>offset = 0</varname>.
- A drawback of this technique is that memory is always
- mapped beginning with its start address.
- </para>
-</sect1>
-
-<sect1 id="wait_for_interrupts">
-<title>Waiting for interrupts</title>
- <para>
- After you successfully mapped your devices memory, you
- can access it like an ordinary array. Usually, you will
- perform some initialization. After that, your hardware
- starts working and will generate an interrupt as soon
- as it's finished, has some data available, or needs your
- attention because an error occurred.
- </para>
- <para>
- <filename>/dev/uioX</filename> is a read-only file. A
- <function>read()</function> will always block until an
- interrupt occurs. There is only one legal value for the
- <varname>count</varname> parameter of
- <function>read()</function>, and that is the size of a
- signed 32 bit integer (4). Any other value for
- <varname>count</varname> causes <function>read()</function>
- to fail. The signed 32 bit integer read is the interrupt
- count of your device. If the value is one more than the value
- you read the last time, everything is OK. If the difference
- is greater than one, you missed interrupts.
- </para>
- <para>
- You can also use <function>select()</function> on
- <filename>/dev/uioX</filename>.
- </para>
-</sect1>
-
-</chapter>
-
-<chapter id="uio_pci_generic" xreflabel="Using Generic driver for PCI cards">
-<?dbhtml filename="uio_pci_generic.html"?>
-<title>Generic PCI UIO driver</title>
- <para>
- The generic driver is a kernel module named uio_pci_generic.
- It can work with any device compliant to PCI 2.3 (circa 2002) and
- any compliant PCI Express device. Using this, you only need to
- write the userspace driver, removing the need to write
- a hardware-specific kernel module.
- </para>
-
-<sect1 id="uio_pci_generic_binding">
-<title>Making the driver recognize the device</title>
- <para>
-Since the driver does not declare any device ids, it will not get loaded
-automatically and will not automatically bind to any devices, you must load it
-and allocate id to the driver yourself. For example:
- <programlisting>
- modprobe uio_pci_generic
- echo &quot;8086 10f5&quot; &gt; /sys/bus/pci/drivers/uio_pci_generic/new_id
- </programlisting>
- </para>
- <para>
-If there already is a hardware specific kernel driver for your device, the
-generic driver still won't bind to it, in this case if you want to use the
-generic driver (why would you?) you'll have to manually unbind the hardware
-specific driver and bind the generic driver, like this:
- <programlisting>
- echo -n 0000:00:19.0 &gt; /sys/bus/pci/drivers/e1000e/unbind
- echo -n 0000:00:19.0 &gt; /sys/bus/pci/drivers/uio_pci_generic/bind
- </programlisting>
- </para>
- <para>
-You can verify that the device has been bound to the driver
-by looking for it in sysfs, for example like the following:
- <programlisting>
- ls -l /sys/bus/pci/devices/0000:00:19.0/driver
- </programlisting>
-Which if successful should print
- <programlisting>
- .../0000:00:19.0/driver -&gt; ../../../bus/pci/drivers/uio_pci_generic
- </programlisting>
-Note that the generic driver will not bind to old PCI 2.2 devices.
-If binding the device failed, run the following command:
- <programlisting>
- dmesg
- </programlisting>
-and look in the output for failure reasons
- </para>
-</sect1>
-
-<sect1 id="uio_pci_generic_internals">
-<title>Things to know about uio_pci_generic</title>
- <para>
-Interrupts are handled using the Interrupt Disable bit in the PCI command
-register and Interrupt Status bit in the PCI status register. All devices
-compliant to PCI 2.3 (circa 2002) and all compliant PCI Express devices should
-support these bits. uio_pci_generic detects this support, and won't bind to
-devices which do not support the Interrupt Disable Bit in the command register.
- </para>
- <para>
-On each interrupt, uio_pci_generic sets the Interrupt Disable bit.
-This prevents the device from generating further interrupts
-until the bit is cleared. The userspace driver should clear this
-bit before blocking and waiting for more interrupts.
- </para>
-</sect1>
-<sect1 id="uio_pci_generic_userspace">
-<title>Writing userspace driver using uio_pci_generic</title>
- <para>
-Userspace driver can use pci sysfs interface, or the
-libpci libray that wraps it, to talk to the device and to
-re-enable interrupts by writing to the command register.
- </para>
-</sect1>
-<sect1 id="uio_pci_generic_example">
-<title>Example code using uio_pci_generic</title>
- <para>
-Here is some sample userspace driver code using uio_pci_generic:
-<programlisting>
-#include &lt;stdlib.h&gt;
-#include &lt;stdio.h&gt;
-#include &lt;unistd.h&gt;
-#include &lt;sys/types.h&gt;
-#include &lt;sys/stat.h&gt;
-#include &lt;fcntl.h&gt;
-#include &lt;errno.h&gt;
-
-int main()
-{
- int uiofd;
- int configfd;
- int err;
- int i;
- unsigned icount;
- unsigned char command_high;
-
- uiofd = open(&quot;/dev/uio0&quot;, O_RDONLY);
- if (uiofd &lt; 0) {
- perror(&quot;uio open:&quot;);
- return errno;
- }
- configfd = open(&quot;/sys/class/uio/uio0/device/config&quot;, O_RDWR);
- if (uiofd &lt; 0) {
- perror(&quot;config open:&quot;);
- return errno;
- }
-
- /* Read and cache command value */
- err = pread(configfd, &amp;command_high, 1, 5);
- if (err != 1) {
- perror(&quot;command config read:&quot;);
- return errno;
- }
- command_high &amp;= ~0x4;
-
- for(i = 0;; ++i) {
- /* Print out a message, for debugging. */
- if (i == 0)
- fprintf(stderr, &quot;Started uio test driver.\n&quot;);
- else
- fprintf(stderr, &quot;Interrupts: %d\n&quot;, icount);
-
- /****************************************/
- /* Here we got an interrupt from the
- device. Do something to it. */
- /****************************************/
-
- /* Re-enable interrupts. */
- err = pwrite(configfd, &amp;command_high, 1, 5);
- if (err != 1) {
- perror(&quot;config write:&quot;);
- break;
- }
-
- /* Wait for next interrupt. */
- err = read(uiofd, &amp;icount, 4);
- if (err != 4) {
- perror(&quot;uio read:&quot;);
- break;
- }
-
- }
- return errno;
-}
-
-</programlisting>
- </para>
-</sect1>
-
-</chapter>
-
-<appendix id="app1">
-<title>Further information</title>
-<itemizedlist>
- <listitem><para>
- <ulink url="http://www.osadl.org">
- OSADL homepage.</ulink>
- </para></listitem>
- <listitem><para>
- <ulink url="http://www.linutronix.de">
- Linutronix homepage.</ulink>
- </para></listitem>
-</itemizedlist>
-</appendix>
-
-</book>