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Message-Id: <200704300018.35064.hjk@linutronix.de> Date: Mon, 30 Apr 2007 00:18:34 +0200 From: Hans-Jürgen Koch <hjk@...utronix.de> To: tglx@...utronix.de Cc: Alan Cox <alan@...rguk.ukuu.org.uk>, Greg Kroah-Hartman <gregkh@...e.de>, linux-kernel@...r.kernel.org, torvalds@...l.org, Benedikt Spranger <b.spranger@...utronix.de> Subject: Re: Flaws with "UIO: Add the User IO core code" (with patch) 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> - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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