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