</abstract>
<revhistory>
+ <revision>
+ <revnumber>0.8</revnumber>
+ <date>2008-12-24</date>
+ <authorinitials>hjk</authorinitials>
+ <revremark>Added name attributes in mem and portio sysfs directories.
+ </revremark>
+ </revision>
+ <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>
appear if the size of the mapping is not 0.
</para>
<para>
- Each <filename>mapX/</filename> directory contains two read-only files
- that show start address and size of the memory:
+ Each <filename>mapX/</filename> directory contains four read-only files
+ that show attributes of the memory:
</para>
<itemizedlist>
+<listitem>
+ <para>
+ <filename>name</filename>: A string identifier for this mapping. This
+ is optional, the string can be empty. Drivers can set this to make it
+ easier for userspace to find the correct mapping.
+ </para>
+</listitem>
<listitem>
<para>
<filename>addr</filename>: The address of memory that can be mapped.
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>
<filename>/sys/class/uio/uioX/portio/</filename>.
</para>
<para>
- Each <filename>portX/</filename> directory contains three read-only
- files that show start, size, and type of the port region:
+ Each <filename>portX/</filename> directory contains four read-only
+ files that show name, start, size, and type of the port region:
</para>
<itemizedlist>
+<listitem>
+ <para>
+ <filename>name</filename>: A string identifier for this port region.
+ The string is optional and can be empty. Drivers can set it to make it
+ easier for userspace to find a certain port region.
+ </para>
+</listitem>
<listitem>
<para>
<filename>start</filename>: The first port of this region.
</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">
projects / linux-2.6-omap-h63xx.git / blobdiff