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diff --git a/kernel/Documentation/DocBook/uio-howto.tmpl b/kernel/Documentation/DocBook/uio-howto.tmpl new file mode 100644 index 000000000..cd0e452df --- /dev/null +++ b/kernel/Documentation/DocBook/uio-howto.tmpl @@ -0,0 +1,1050 @@ +<?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> |