827 строки
29 KiB
XML
827 строки
29 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd" []>
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<book id="index">
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<bookinfo>
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<title>The Userspace I/O HOWTO</title>
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<author>
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<firstname>Hans-Jürgen</firstname>
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<surname>Koch</surname>
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<authorblurb><para>Linux developer, Linutronix</para></authorblurb>
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<affiliation>
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<orgname>
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<ulink url="http://www.linutronix.de">Linutronix</ulink>
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</orgname>
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<address>
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<email>hjk@linutronix.de</email>
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</address>
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</affiliation>
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</author>
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<copyright>
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<year>2006-2008</year>
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<holder>Hans-Jürgen Koch.</holder>
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</copyright>
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<legalnotice>
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<para>
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This documentation is Free Software licensed under the terms of the
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GPL version 2.
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</para>
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</legalnotice>
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<pubdate>2006-12-11</pubdate>
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<abstract>
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<para>This HOWTO describes concept and usage of Linux kernel's
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Userspace I/O system.</para>
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</abstract>
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<revhistory>
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<revision>
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<revnumber>0.8</revnumber>
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<date>2008-12-24</date>
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<authorinitials>hjk</authorinitials>
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<revremark>Added name attributes in mem and portio sysfs directories.
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</revremark>
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</revision>
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<revision>
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<revnumber>0.7</revnumber>
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<date>2008-12-23</date>
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<authorinitials>hjk</authorinitials>
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<revremark>Added generic platform drivers and offset attribute.</revremark>
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</revision>
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<revision>
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<revnumber>0.6</revnumber>
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<date>2008-12-05</date>
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<authorinitials>hjk</authorinitials>
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<revremark>Added description of portio sysfs attributes.</revremark>
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</revision>
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<revision>
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<revnumber>0.5</revnumber>
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<date>2008-05-22</date>
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<authorinitials>hjk</authorinitials>
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<revremark>Added description of write() function.</revremark>
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</revision>
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<revision>
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<revnumber>0.4</revnumber>
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<date>2007-11-26</date>
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<authorinitials>hjk</authorinitials>
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<revremark>Removed section about uio_dummy.</revremark>
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</revision>
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<revision>
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<revnumber>0.3</revnumber>
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<date>2007-04-29</date>
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<authorinitials>hjk</authorinitials>
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<revremark>Added section about userspace drivers.</revremark>
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</revision>
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<revision>
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<revnumber>0.2</revnumber>
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<date>2007-02-13</date>
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<authorinitials>hjk</authorinitials>
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<revremark>Update after multiple mappings were added.</revremark>
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</revision>
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<revision>
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<revnumber>0.1</revnumber>
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<date>2006-12-11</date>
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<authorinitials>hjk</authorinitials>
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<revremark>First draft.</revremark>
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</revision>
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</revhistory>
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</bookinfo>
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<chapter id="aboutthisdoc">
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<?dbhtml filename="aboutthis.html"?>
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<title>About this document</title>
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<sect1 id="translations">
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<?dbhtml filename="translations.html"?>
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<title>Translations</title>
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<para>If you know of any translations for this document, or you are
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interested in translating it, please email me
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<email>hjk@linutronix.de</email>.
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</para>
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</sect1>
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<sect1 id="preface">
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<title>Preface</title>
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<para>
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For many types of devices, creating a Linux kernel driver is
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overkill. All that is really needed is some way to handle an
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interrupt and provide access to the memory space of the
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device. The logic of controlling the device does not
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necessarily have to be within the kernel, as the device does
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not need to take advantage of any of other resources that the
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kernel provides. One such common class of devices that are
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like this are for industrial I/O cards.
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</para>
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<para>
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To address this situation, the userspace I/O system (UIO) was
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designed. For typical industrial I/O cards, only a very small
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kernel module is needed. The main part of the driver will run in
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user space. This simplifies development and reduces the risk of
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serious bugs within a kernel module.
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</para>
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<para>
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Please note that UIO is not an universal driver interface. Devices
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that are already handled well by other kernel subsystems (like
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networking or serial or USB) are no candidates for an UIO driver.
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Hardware that is ideally suited for an UIO driver fulfills all of
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the following:
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</para>
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<itemizedlist>
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<listitem>
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<para>The device has memory that can be mapped. The device can be
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controlled completely by writing to this memory.</para>
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</listitem>
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<listitem>
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<para>The device usually generates interrupts.</para>
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</listitem>
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<listitem>
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<para>The device does not fit into one of the standard kernel
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subsystems.</para>
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</listitem>
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</itemizedlist>
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</sect1>
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<sect1 id="thanks">
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<title>Acknowledgments</title>
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<para>I'd like to thank Thomas Gleixner and Benedikt Spranger of
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Linutronix, who have not only written most of the UIO code, but also
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helped greatly writing this HOWTO by giving me all kinds of background
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information.</para>
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</sect1>
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<sect1 id="feedback">
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<title>Feedback</title>
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<para>Find something wrong with this document? (Or perhaps something
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right?) I would love to hear from you. Please email me at
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<email>hjk@linutronix.de</email>.</para>
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</sect1>
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</chapter>
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<chapter id="about">
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<?dbhtml filename="about.html"?>
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<title>About UIO</title>
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<para>If you use UIO for your card's driver, here's what you get:</para>
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<itemizedlist>
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<listitem>
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<para>only one small kernel module to write and maintain.</para>
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</listitem>
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<listitem>
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<para>develop the main part of your driver in user space,
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with all the tools and libraries you're used to.</para>
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</listitem>
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<listitem>
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<para>bugs in your driver won't crash the kernel.</para>
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</listitem>
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<listitem>
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<para>updates of your driver can take place without recompiling
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the kernel.</para>
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</listitem>
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</itemizedlist>
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<sect1 id="how_uio_works">
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<title>How UIO works</title>
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<para>
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Each UIO device is accessed through a device file and several
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sysfs attribute files. The device file will be called
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<filename>/dev/uio0</filename> for the first device, and
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<filename>/dev/uio1</filename>, <filename>/dev/uio2</filename>
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and so on for subsequent devices.
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</para>
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<para><filename>/dev/uioX</filename> is used to access the
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address space of the card. Just use
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<function>mmap()</function> to access registers or RAM
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locations of your card.
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</para>
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<para>
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Interrupts are handled by reading from
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<filename>/dev/uioX</filename>. A blocking
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<function>read()</function> from
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<filename>/dev/uioX</filename> will return as soon as an
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interrupt occurs. You can also use
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<function>select()</function> on
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<filename>/dev/uioX</filename> to wait for an interrupt. The
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integer value read from <filename>/dev/uioX</filename>
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represents the total interrupt count. You can use this number
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to figure out if you missed some interrupts.
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</para>
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<para>
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For some hardware that has more than one interrupt source internally,
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but not separate IRQ mask and status registers, there might be
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situations where userspace cannot determine what the interrupt source
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was if the kernel handler disables them by writing to the chip's IRQ
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register. In such a case, the kernel has to disable the IRQ completely
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to leave the chip's register untouched. Now the userspace part can
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determine the cause of the interrupt, but it cannot re-enable
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interrupts. Another cornercase is chips where re-enabling interrupts
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is a read-modify-write operation to a combined IRQ status/acknowledge
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register. This would be racy if a new interrupt occurred
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simultaneously.
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</para>
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<para>
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To address these problems, UIO also implements a write() function. It
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is normally not used and can be ignored for hardware that has only a
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single interrupt source or has separate IRQ mask and status registers.
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If you need it, however, a write to <filename>/dev/uioX</filename>
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will call the <function>irqcontrol()</function> function implemented
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by the driver. You have to write a 32-bit value that is usually either
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0 or 1 to disable or enable interrupts. If a driver does not implement
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<function>irqcontrol()</function>, <function>write()</function> will
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return with <varname>-ENOSYS</varname>.
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</para>
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<para>
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To handle interrupts properly, your custom kernel module can
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provide its own interrupt handler. It will automatically be
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called by the built-in handler.
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</para>
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<para>
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For cards that don't generate interrupts but need to be
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polled, there is the possibility to set up a timer that
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triggers the interrupt handler at configurable time intervals.
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This interrupt simulation is done by calling
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<function>uio_event_notify()</function>
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from the timer's event handler.
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</para>
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<para>
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Each driver provides attributes that are used to read or write
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variables. These attributes are accessible through sysfs
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files. A custom kernel driver module can add its own
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attributes to the device owned by the uio driver, but not added
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to the UIO device itself at this time. This might change in the
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future if it would be found to be useful.
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</para>
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<para>
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The following standard attributes are provided by the UIO
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framework:
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</para>
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<itemizedlist>
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<listitem>
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<para>
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<filename>name</filename>: The name of your device. It is
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recommended to use the name of your kernel module for this.
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</para>
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</listitem>
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<listitem>
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<para>
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<filename>version</filename>: A version string defined by your
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driver. This allows the user space part of your driver to deal
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with different versions of the kernel module.
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</para>
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</listitem>
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<listitem>
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<para>
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<filename>event</filename>: The total number of interrupts
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handled by the driver since the last time the device node was
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read.
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</para>
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</listitem>
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</itemizedlist>
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<para>
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These attributes appear under the
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<filename>/sys/class/uio/uioX</filename> directory. Please
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note that this directory might be a symlink, and not a real
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directory. Any userspace code that accesses it must be able
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to handle this.
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</para>
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<para>
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Each UIO device can make one or more memory regions available for
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memory mapping. This is necessary because some industrial I/O cards
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require access to more than one PCI memory region in a driver.
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</para>
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<para>
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Each mapping has its own directory in sysfs, the first mapping
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appears as <filename>/sys/class/uio/uioX/maps/map0/</filename>.
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Subsequent mappings create directories <filename>map1/</filename>,
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<filename>map2/</filename>, and so on. These directories will only
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appear if the size of the mapping is not 0.
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</para>
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<para>
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Each <filename>mapX/</filename> directory contains four read-only files
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that show attributes of the memory:
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</para>
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<itemizedlist>
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<listitem>
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<para>
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<filename>name</filename>: A string identifier for this mapping. This
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is optional, the string can be empty. Drivers can set this to make it
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easier for userspace to find the correct mapping.
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</para>
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</listitem>
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<listitem>
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<para>
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<filename>addr</filename>: The address of memory that can be mapped.
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</para>
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</listitem>
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<listitem>
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<para>
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<filename>size</filename>: The size, in bytes, of the memory
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pointed to by addr.
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</para>
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</listitem>
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<listitem>
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<para>
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<filename>offset</filename>: The offset, in bytes, that has to be
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added to the pointer returned by <function>mmap()</function> to get
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to the actual device memory. This is important if the device's memory
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is not page aligned. Remember that pointers returned by
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<function>mmap()</function> are always page aligned, so it is good
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style to always add this offset.
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</para>
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</listitem>
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</itemizedlist>
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<para>
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From userspace, the different mappings are distinguished by adjusting
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the <varname>offset</varname> parameter of the
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<function>mmap()</function> call. To map the memory of mapping N, you
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have to use N times the page size as your offset:
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</para>
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<programlisting format="linespecific">
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offset = N * getpagesize();
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</programlisting>
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<para>
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Sometimes there is hardware with memory-like regions that can not be
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mapped with the technique described here, but there are still ways to
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access them from userspace. The most common example are x86 ioports.
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On x86 systems, userspace can access these ioports using
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<function>ioperm()</function>, <function>iopl()</function>,
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<function>inb()</function>, <function>outb()</function>, and similar
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functions.
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</para>
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<para>
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Since these ioport regions can not be mapped, they will not appear under
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<filename>/sys/class/uio/uioX/maps/</filename> like the normal memory
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described above. Without information about the port regions a hardware
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has to offer, it becomes difficult for the userspace part of the
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driver to find out which ports belong to which UIO device.
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</para>
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<para>
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To address this situation, the new directory
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<filename>/sys/class/uio/uioX/portio/</filename> was added. It only
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exists if the driver wants to pass information about one or more port
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regions to userspace. If that is the case, subdirectories named
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<filename>port0</filename>, <filename>port1</filename>, and so on,
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will appear underneath
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<filename>/sys/class/uio/uioX/portio/</filename>.
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</para>
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<para>
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Each <filename>portX/</filename> directory contains four read-only
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files that show name, start, size, and type of the port region:
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</para>
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<itemizedlist>
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<listitem>
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<para>
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<filename>name</filename>: A string identifier for this port region.
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The string is optional and can be empty. Drivers can set it to make it
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easier for userspace to find a certain port region.
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</para>
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</listitem>
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<listitem>
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<para>
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<filename>start</filename>: The first port of this region.
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</para>
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</listitem>
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<listitem>
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<para>
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<filename>size</filename>: The number of ports in this region.
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</para>
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</listitem>
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<listitem>
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<para>
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<filename>porttype</filename>: A string describing the type of port.
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</para>
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</listitem>
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</itemizedlist>
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|
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</sect1>
|
|
</chapter>
|
|
|
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<chapter id="custom_kernel_module" xreflabel="Writing your own kernel module">
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<?dbhtml filename="custom_kernel_module.html"?>
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<title>Writing your own kernel module</title>
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<para>
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Please have a look at <filename>uio_cif.c</filename> as an
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example. The following paragraphs explain the different
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sections of this file.
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</para>
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<sect1 id="uio_info">
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<title>struct uio_info</title>
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<para>
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This structure tells the framework the details of your driver,
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Some of the members are required, others are optional.
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</para>
|
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|
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<itemizedlist>
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<listitem><para>
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<varname>const char *name</varname>: Required. The name of your driver as
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it will appear in sysfs. I recommend using the name of your module for this.
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</para></listitem>
|
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|
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<listitem><para>
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<varname>const char *version</varname>: Required. This string appears in
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<filename>/sys/class/uio/uioX/version</filename>.
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</para></listitem>
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|
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<listitem><para>
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<varname>struct uio_mem mem[ MAX_UIO_MAPS ]</varname>: Required if you
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have memory that can be mapped with <function>mmap()</function>. For each
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mapping you need to fill one of the <varname>uio_mem</varname> structures.
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See the description below for details.
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</para></listitem>
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<listitem><para>
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<varname>struct uio_port port[ MAX_UIO_PORTS_REGIONS ]</varname>: Required
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if you want to pass information about ioports to userspace. For each port
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region you need to fill one of the <varname>uio_port</varname> structures.
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See the description below for details.
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</para></listitem>
|
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<listitem><para>
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<varname>long irq</varname>: Required. If your hardware generates an
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interrupt, it's your modules task to determine the irq number during
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initialization. If you don't have a hardware generated interrupt but
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want to trigger the interrupt handler in some other way, set
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<varname>irq</varname> to <varname>UIO_IRQ_CUSTOM</varname>.
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If you had no interrupt at all, you could set
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<varname>irq</varname> to <varname>UIO_IRQ_NONE</varname>, though this
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rarely makes sense.
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</para></listitem>
|
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|
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<listitem><para>
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<varname>unsigned long irq_flags</varname>: Required if you've set
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<varname>irq</varname> to a hardware interrupt number. The flags given
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here will be used in the call to <function>request_irq()</function>.
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</para></listitem>
|
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|
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<listitem><para>
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<varname>int (*mmap)(struct uio_info *info, struct vm_area_struct
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*vma)</varname>: Optional. If you need a special
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<function>mmap()</function> function, you can set it here. If this
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pointer is not NULL, your <function>mmap()</function> will be called
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instead of the built-in one.
|
|
</para></listitem>
|
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|
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<listitem><para>
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<varname>int (*open)(struct uio_info *info, struct inode *inode)
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</varname>: Optional. You might want to have your own
|
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<function>open()</function>, e.g. to enable interrupts only when your
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device is actually used.
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</para></listitem>
|
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|
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<listitem><para>
|
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<varname>int (*release)(struct uio_info *info, struct inode *inode)
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|
</varname>: Optional. If you define your own
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<function>open()</function>, you will probably also want a custom
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<function>release()</function> function.
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</para></listitem>
|
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|
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<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>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>unsigned long 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>kobj</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 occured.
|
|
</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>
|
|
|
|
<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>
|