Add uio_dmem_genirq description to UIO documentation

Signed-off-by: Damian Hobson-Garcia <dhobsong@igel.co.jp>
Signed-off-by: "Hans J. Koch" <hjk@hansjkoch.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/DocBook/uio-howto.tmpl

@@ -719,6 +719,62 @@ framework to set up sysfs files for this region. Simply leave it alone.
 	</para>
 </sect1>
 
+<sect1 id="using uio_dmem_genirq">
+<title>Using uio_dmem_genirq for platform devices</title>
+	<para>
+	In addition to statically allocated memory ranges, they may also be
+	a desire to use dynamically allocated regions in a user space driver.
+	In particular, being able to access memory made available through the
+	dma-mapping API, may be particularly useful.  The
+	<varname>uio_dmem_genirq</varname> driver provides a way to accomplish
+	this.
+	</para>
+	<para>
+	This driver is used in a similar manner to the
+	<varname>"uio_pdrv_genirq"</varname> driver with respect to interrupt
+	configuration and handling.
+	</para>
+	<para>
+	Set the <varname>.name</varname> element of
+	<varname>struct platform_device</varname> to
+	<varname>"uio_dmem_genirq"</varname> to use this driver.
+	</para>
+	<para>
+	When using this driver, fill in the <varname>.platform_data</varname>
+	element of <varname>struct platform_device</varname>, which is of type
+	<varname>struct uio_dmem_genirq_pdata</varname> and which contains the
+	following elements:
+	</para>
+	<itemizedlist>
+	<listitem><varname>struct uio_info uioinfo</varname>: The same
+	structure used as the  <varname>uio_pdrv_genirq</varname> platform
+	data</listitem>
+	<listitem><varname>unsigned int *dynamic_region_sizes</varname>:
+	Pointer to list of sizes of dynamic memory regions to be mapped into
+	user space.
+	</listitem>
+	<listitem><varname>unsigned int num_dynamic_regions</varname>:
+	Number of elements in <varname>dynamic_region_sizes</varname> array.
+	</listitem>
+	</itemizedlist>
+	<para>
+	The dynamic regions defined in the platform data will be appended to
+	the <varname> mem[] </varname> array after the platform device
+	resources, which implies that the total number of static and dynamic
+	memory regions cannot exceed <varname>MAX_UIO_MAPS</varname>.
+	</para>
+	<para>
+	The dynamic memory regions will be allocated when the UIO device file,
+	<varname>/dev/uioX</varname> is opened.
+	Simiar to static memory resources, the memory region information for
+	dynamic regions is then visible via sysfs at
+	<varname>/sys/class/uio/uioX/maps/mapY/*</varname>.
+	The dynmaic memory regions will be freed when the UIO device file is
+	closed. When no processes are holding the device file open, the address
+	returned to userspace is DMA_ERROR_CODE.
+	</para>
+</sect1>
+
 </chapter>
 
 <chapter id="userspace_driver" xreflabel="Writing a driver in user space">