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UIO: Add missing documentation of features added recently

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The following features were added to the UIO framework in the near past:

* Generic drivers for platform devices (uio_pdrv, uio_pdrv_genirq)
* an "offset" sysfs attribute for memory mappings

Unfortunately, all this went in without documentation (won't happen again...)

This patch updates UIO documentation.

Signed-off-by: Hans J. Koch <hjk@linutronix.de>
Acked-by: Uwe Kleine-König <ukleinek@strlen.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
This commit is contained in:
Hans J. Koch 2009-01-07 00:12:37 +01:00 committed by Greg Kroah-Hartman
parent 720893fd5f
commit 6a1b699678
1 changed files with 88 additions and 0 deletions
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88
Documentation/DocBook/uio-howto.tmpl
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@ -41,6 +41,12 @@ GPL version 2.
</abstract>
<revhistory>
<revision>
<revnumber>0.7</revnumber>
<date>2008-12-23</date>
<authorinitials>hjk</authorinitials>
<revremark>Added generic platform drivers and offset attribute.</revremark>
</revision>
<revision>
<revnumber>0.6</revnumber>
<date>2008-12-05</date>
@ -312,6 +318,16 @@ interested in translating it, please email me
pointed to by addr.
</para>
</listitem>
<listitem>
<para>
<filename>offset</filename>: The offset, in bytes, that has to be
added to the pointer returned by <function>mmap()</function> to get
to the actual device memory. This is important if the device's memory
is not page aligned. Remember that pointers returned by
<function>mmap()</function> are always page aligned, so it is good
style to always add this offset.
</para>
</listitem>
</itemizedlist>
<para>
@ -594,6 +610,78 @@ framework to set up sysfs files for this region. Simply leave it alone.
</para>
</sect1>
<sect1 id="using_uio_pdrv">
<title>Using uio_pdrv for platform devices</title>
<para>
In many cases, UIO drivers for platform devices can be handled in a
generic way. In the same place where you define your
<varname>struct platform_device</varname>, you simply also implement
your interrupt handler and fill your
<varname>struct uio_info</varname>. A pointer to this
<varname>struct uio_info</varname> is then used as
<varname>platform_data</varname> for your platform device.
</para>
<para>
You also need to set up an array of <varname>struct resource</varname>
containing addresses and sizes of your memory mappings. This
information is passed to the driver using the
<varname>.resource</varname> and <varname>.num_resources</varname>
elements of <varname>struct platform_device</varname>.
</para>
<para>
You now have to set the <varname>.name</varname> element of
<varname>struct platform_device</varname> to
<varname>"uio_pdrv"</varname> to use the generic UIO platform device
driver. This driver will fill the <varname>mem[]</varname> array
according to the resources given, and register the device.
</para>
<para>
The advantage of this approach is that you only have to edit a file
you need to edit anyway. You do not have to create an extra driver.
</para>
</sect1>
<sect1 id="using_uio_pdrv_genirq">
<title>Using uio_pdrv_genirq for platform devices</title>
<para>
Especially in embedded devices, you frequently find chips where the
irq pin is tied to its own dedicated interrupt line. In such cases,
where you can be really sure the interrupt is not shared, we can take
the concept of <varname>uio_pdrv</varname> one step further and use a
generic interrupt handler. That's what
<varname>uio_pdrv_genirq</varname> does.
</para>
<para>
The setup for this driver is the same as described above for
<varname>uio_pdrv</varname>, except that you do not implement an
interrupt handler. The <varname>.handler</varname> element of
<varname>struct uio_info</varname> must remain
<varname>NULL</varname>. The <varname>.irq_flags</varname> element
must not contain <varname>IRQF_SHARED</varname>.
</para>
<para>
You will set the <varname>.name</varname> element of
<varname>struct platform_device</varname> to
<varname>"uio_pdrv_genirq"</varname> to use this driver.
</para>
<para>
The generic interrupt handler of <varname>uio_pdrv_genirq</varname>
will simply disable the interrupt line using
<function>disable_irq_nosync()</function>. After doing its work,
userspace can reenable the interrupt by writing 0x00000001 to the UIO
device file. The driver already implements an
<function>irq_control()</function> to make this possible, you must not
implement your own.
</para>
<para>
Using <varname>uio_pdrv_genirq</varname> not only saves a few lines of
interrupt handler code. You also do not need to know anything about
the chip's internal registers to create the kernel part of the driver.
All you need to know is the irq number of the pin the chip is
connected to.
</para>
</sect1>
</chapter>
<chapter id="userspace_driver" xreflabel="Writing a driver in user space">