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Subject[PATCH 3/6] UIO: fix up the UIO documentation
From: Hans J Koch <>

Remove references to the old uio_dummy demo module from UIO documentation.
Add a small paragraph to make it clearer that UIO is not a universal driver

Signed-off-by: Hans J Koch <>
Signed-off-by: Greg Kroah-Hartman <>
Documentation/DocBook/uio-howto.tmpl | 90 ++++++++++++----------------------
1 files changed, 32 insertions(+), 58 deletions(-)

diff --git a/Documentation/DocBook/uio-howto.tmpl b/Documentation/DocBook/uio-howto.tmpl
index c119484..fdd7f4f 100644
--- a/Documentation/DocBook/uio-howto.tmpl
+++ b/Documentation/DocBook/uio-howto.tmpl
@@ -30,6 +30,12 @@

+ <revnumber>0.4</revnumber>
+ <date>2007-11-26</date>
+ <authorinitials>hjk</authorinitials>
+ <revremark>Removed section about uio_dummy.</revremark>
+ </revision>
+ <revision>
@@ -94,6 +100,26 @@ interested in translating it, please email me
user space. This simplifies development and reduces the risk of
serious bugs within a kernel module.
+ <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>
+ <para>The device has memory that can be mapped. The device can be
+ controlled completely by writing to this memory.</para>
+ <para>The device usually generates interrupts.</para>
+ <para>The device does not fit into one of the standard kernel
+ subsystems.</para>

<sect1 id="thanks">
@@ -174,8 +200,9 @@ interested in translating it, please email me
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.
+ This interrupt simulation is done by calling
+ <function>uio_event_notify()</function>
+ from the timer's event handler.

@@ -263,63 +290,11 @@ offset = N * getpagesize();

-<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
- <para>
- Use <function>cat count</function> to see how the interrupt
- frequency changes.
- </para>
<chapter id="custom_kernel_module" xreflabel="Writing your own kernel module">
<?dbhtml filename="custom_kernel_module.html"?>
<title>Writing your own kernel module</title>
- Please have a look at <filename>uio_dummy.c</filename> as an
+ Please have a look at <filename>uio_cif.c</filename> as an
example. The following paragraphs explain the different
sections of this file.
@@ -354,9 +329,8 @@ See the description below for details.
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_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.
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