Merge master.kernel.org:/pub/scm/linux/kernel/git/gregkh/uio-2.6

!Edrivers/pnp/manager.c

!Edrivers/pnp/support.c

     </sect1>

     <sect1><title>Userspace IO devices</title>

!Edrivers/uio/uio.c

!Iinclude/linux/uio_driver.h

     </sect1>

  </chapter>

  <chapter id="blkdev">

<?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@linutronix.de</email>

	</address>

    </affiliation>

</author>

<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>0.3</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="about.html"?>

<title>About this document</title>

<sect1 id="copyright">

<?dbhtml filename="copyright.html"?>

<title>Copyright and License</title>

<para>

      Copyright (c) 2006 by Hans-Jürgen Koch.</para>

<para>

This documentation is Free Software licensed under the terms of the

GPL version 2.

</para>

</sect1>

<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@linutronix.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>

</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@linutronix.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>

<listitem>

	<para>if you need to keep some parts of your driver closed source,

	you can do so without violating the GPL license on 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>

	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.

	See <filename>drivers/uio/uio_dummy.c</filename> for an

	example of this technique.

	</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 two read-only files

	that show start address and size of the memory:

</para>

<itemizedlist>

<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>

</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>

</sect1>

</chapter>

<chapter id="using-uio_dummy" xreflabel="Using uio_dummy">

<?dbhtml filename="using-uio_dummy.html"?>

<title>Using uio_dummy</title>

	<para>

	Well, there is no real use for uio_dummy. Its only purpose is

	to test most parts of the UIO system (everything except

	hardware interrupts), and to serve as an example for the

	kernel module that you will have to write yourself.

	</para>

<sect1 id="what_uio_dummy_does">

<title>What uio_dummy does</title>

	<para>

	The kernel module <filename>uio_dummy.ko</filename> creates a

	device that uses a timer to generate periodic interrupts. The

	interrupt handler does nothing but increment a counter. The

	driver adds two custom attributes, <varname>count</varname>

	and <varname>freq</varname>, that appear under

	<filename>/sys/devices/platform/uio_dummy/</filename>.

	</para>

	<para>

	The attribute <varname>count</varname> can be read and

	written.  The associated file

	<filename>/sys/devices/platform/uio_dummy/count</filename>

	appears as a normal text file and contains the total number of

	timer interrupts. If you look at it (e.g. using

	<function>cat</function>), you'll notice it is slowly counting

	up.

	</para>

	<para>

	The attribute <varname>freq</varname> can be read and written.

	The content of

	<filename>/sys/devices/platform/uio_dummy/freq</filename>

	represents the number of system timer ticks between two timer

	interrupts. The default value of <varname>freq</varname> is

	the value of the kernel variable <varname>HZ</varname>, which

	gives you an interval of one second. Lower values will

	increase the frequency. Try the following:

	</para>

<programlisting format="linespecific">

cd /sys/devices/platform/uio_dummy/

echo 100 > freq

</programlisting>

	<para>

	Use <function>cat count</function> to see how the interrupt

	frequency changes.

	</para>

</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_dummy.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>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>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>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>. The

uio_dummy module does this as it triggers the event mechanism in a timer

routine. 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>

</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>

</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>

</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>

source "drivers/kvm/Kconfig"

source "drivers/uio/Kconfig"

endmenu

obj-$(CONFIG_FUSION)		+= message/

obj-$(CONFIG_FIREWIRE)		+= firewire/

obj-$(CONFIG_IEEE1394)		+= ieee1394/

obj-$(CONFIG_UIO)		+= uio/

obj-y				+= cdrom/

obj-y				+= auxdisplay/

obj-$(CONFIG_MTD)		+= mtd/

menu "Userspace I/O"

	depends on !S390

config UIO

	tristate "Userspace I/O drivers"

	default n

	help

	  Enable this to allow the userspace driver core code to be

	  built.  This code allows userspace programs easy access to

	  kernel interrupts and memory locations, allowing some drivers

	  to be written in userspace.  Note that a small kernel driver

	  is also required for interrupt handling to work properly.

	  If you don't know what to do here, say N.

config UIO_CIF

	tristate "generic Hilscher CIF Card driver"

	depends on UIO && PCI

	default n

	help

	  Driver for Hilscher CIF DeviceNet and Profibus cards.  This

	  driver requires a userspace component that handles all of the

	  heavy lifting and can be found at:

	  	http://www.osadl.org/projects/downloads/UIO/user/cif-*

	  To compile this driver as a module, choose M here: the module

	  will be called uio_cif.

endmenu