Re: Flaws with "UIO: Add the User IO core code" (with patch)

[Hans-Jürgen Koch <hjk@linutronix.de>]

Am Samstag 28 April 2007 23:14 schrieb Hans-Jürgen Koch:
> Am Samstag 28 April 2007 23:08 schrieb Thomas Gleixner:
> > On Sat, 2007-04-28 at 23:03 +0200, Hans-Jürgen Koch wrote:
> > > Am Samstag 28 April 2007 22:24 schrieb Alan Cox:
> > > > > > AFAIK we don't currently have any platform that runs binaries with
> > > > > > different sizes of "int" but this is a) an unsigned value anyway, and b)
> > > > > > should be a fixed type (eg u32)
> > > > > 
> > > > > I reviewed the code once more and find it OK. There is only one legal
> > > > > value for the parameter "count" of uio_read(), and that's sizeof(int).
> > > > 
> > > > If you are a box with multiple supported binary types how big is an
> > > > "int". We use explicit sizes to ensure that uio_read() will work when/if
> > > > we get platforms which support binaries with differing ideas of the size
> > > > of "int". Thus it should use s32 or s64 or similar.
> > > 
> > > Here's a fix to that effect:
> > 
> > Can you please add a matching paragraph to the documentation ?
> > 
> 
> Yes, I'll add a "How to write userspace code" section tomorrow. I'll send a 
> patch as soon as it's ready.
> 
> Hans
>  

Here's the promised update for the documentation:

Hans


Index: linux-2.6.22-rc/Documentation/DocBook/uio-howto.tmpl
===================================================================
--- linux-2.6.22-rc.orig/Documentation/DocBook/uio-howto.tmpl	2007-04-29 22:17:45.000000000 +0200
+++ linux-2.6.22-rc/Documentation/DocBook/uio-howto.tmpl	2007-04-30 00:15:38.000000000 +0200
@@ -30,6 +30,12 @@
 
 <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>
@@ -484,14 +490,121 @@
 
 </sect1>
 
+<sect1 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>
+
+<sect2 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>
+</sect2>
+
+<sect2 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>
+</sect2>
+
+<sect2 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>
+</sect2>
+
+</sect1>
+
 <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>
-	<listitem><para>...</para></listitem>
 </itemizedlist>
 </appendix>
 
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