--- /dev/null
+<?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>resource_size_t 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>
+
+<sect1 id="using-uio_dmem_genirq">
+<title>Using uio_dmem_genirq for platform devices</title>
+ <para>
+ In addition to statically allocated memory ranges, they may also be
+ a desire to use dynamically allocated regions in a user space driver.
+ In particular, being able to access memory made available through the
+ dma-mapping API, may be particularly useful. The
+ <varname>uio_dmem_genirq</varname> driver provides a way to accomplish
+ this.
+ </para>
+ <para>
+ This driver is used in a similar manner to the
+ <varname>"uio_pdrv_genirq"</varname> driver with respect to interrupt
+ configuration and handling.
+ </para>
+ <para>
+ Set the <varname>.name</varname> element of
+ <varname>struct platform_device</varname> to
+ <varname>"uio_dmem_genirq"</varname> to use this driver.
+ </para>
+ <para>
+ When using this driver, fill in the <varname>.platform_data</varname>
+ element of <varname>struct platform_device</varname>, which is of type
+ <varname>struct uio_dmem_genirq_pdata</varname> and which contains the
+ following elements:
+ </para>
+ <itemizedlist>
+ <listitem><para><varname>struct uio_info uioinfo</varname>: The same
+ structure used as the <varname>uio_pdrv_genirq</varname> platform
+ data</para></listitem>
+ <listitem><para><varname>unsigned int *dynamic_region_sizes</varname>:
+ Pointer to list of sizes of dynamic memory regions to be mapped into
+ user space.
+ </para></listitem>
+ <listitem><para><varname>unsigned int num_dynamic_regions</varname>:
+ Number of elements in <varname>dynamic_region_sizes</varname> array.
+ </para></listitem>
+ </itemizedlist>
+ <para>
+ The dynamic regions defined in the platform data will be appended to
+ the <varname> mem[] </varname> array after the platform device
+ resources, which implies that the total number of static and dynamic
+ memory regions cannot exceed <varname>MAX_UIO_MAPS</varname>.
+ </para>
+ <para>
+ The dynamic memory regions will be allocated when the UIO device file,
+ <varname>/dev/uioX</varname> is opened.
+ Similar to static memory resources, the memory region information for
+ dynamic regions is then visible via sysfs at
+ <varname>/sys/class/uio/uioX/maps/mapY/*</varname>.
+ The dynamic memory regions will be freed when the UIO device file is
+ closed. When no processes are holding the device file open, the address
+ returned to userspace is ~0.
+ </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 "8086 10f5" > /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 > /sys/bus/pci/drivers/e1000e/unbind
+ echo -n 0000:00:19.0 > /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 -> ../../../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 <stdlib.h>
+#include <stdio.h>
+#include <unistd.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <errno.h>
+
+int main()
+{
+ int uiofd;
+ int configfd;
+ int err;
+ int i;
+ unsigned icount;
+ unsigned char command_high;
+
+ uiofd = open("/dev/uio0", O_RDONLY);
+ if (uiofd < 0) {
+ perror("uio open:");
+ return errno;
+ }
+ configfd = open("/sys/class/uio/uio0/device/config", O_RDWR);
+ if (configfd < 0) {
+ perror("config open:");
+ return errno;
+ }
+
+ /* Read and cache command value */
+ err = pread(configfd, &command_high, 1, 5);
+ if (err != 1) {
+ perror("command config read:");
+ return errno;
+ }
+ command_high &= ~0x4;
+
+ for(i = 0;; ++i) {
+ /* Print out a message, for debugging. */
+ if (i == 0)
+ fprintf(stderr, "Started uio test driver.\n");
+ else
+ fprintf(stderr, "Interrupts: %d\n", icount);
+
+ /****************************************/
+ /* Here we got an interrupt from the
+ device. Do something to it. */
+ /****************************************/
+
+ /* Re-enable interrupts. */
+ err = pwrite(configfd, &command_high, 1, 5);
+ if (err != 1) {
+ perror("config write:");
+ break;
+ }
+
+ /* Wait for next interrupt. */
+ err = read(uiofd, &icount, 4);
+ if (err != 4) {
+ perror("uio read:");
+ 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>
Code Review / kvmfornfv.git / blobdiff