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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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