[media] v4l: Add subdev selections documentation

Add documentation for V4L2 subdev selection API. This changes also
experimental V4L2 subdev API so that scaling now works through selection API
only.

Signed-off-by: Sakari Ailus <sakari.ailus@iki.fi>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

1 files changed, 228 insertions, 0 deletions

diff --git a/Documentation/DocBook/media/v4l/vidioc-subdev-g-selection.xml b/Documentation/DocBook/media/v4l/vidioc-subdev-g-selection.xml
new file mode 100644
index 00000000000..208e9f0da3f
--- /dev/null
+++ b/Documentation/DocBook/media/v4l/vidioc-subdev-g-selection.xml
@@ -0,0 +1,228 @@
+<refentry id="vidioc-subdev-g-selection">
+  <refmeta>
+    <refentrytitle>ioctl VIDIOC_SUBDEV_G_SELECTION, VIDIOC_SUBDEV_S_SELECTION</refentrytitle>
+    &manvol;
+  </refmeta>
+
+  <refnamediv>
+    <refname>VIDIOC_SUBDEV_G_SELECTION</refname>
+    <refname>VIDIOC_SUBDEV_S_SELECTION</refname>
+    <refpurpose>Get or set selection rectangles on a subdev pad</refpurpose>
+  </refnamediv>
+
+  <refsynopsisdiv>
+    <funcsynopsis>
+      <funcprototype>
+	<funcdef>int <function>ioctl</function></funcdef>
+	<paramdef>int <parameter>fd</parameter></paramdef>
+	<paramdef>int <parameter>request</parameter></paramdef>
+	<paramdef>struct v4l2_subdev_selection *<parameter>argp</parameter></paramdef>
+      </funcprototype>
+    </funcsynopsis>
+  </refsynopsisdiv>
+
+  <refsect1>
+    <title>Arguments</title>
+
+    <variablelist>
+      <varlistentry>
+	<term><parameter>fd</parameter></term>
+	<listitem>
+	  <para>&fd;</para>
+	</listitem>
+      </varlistentry>
+      <varlistentry>
+	<term><parameter>request</parameter></term>
+	<listitem>
+	  <para>VIDIOC_SUBDEV_G_SELECTION, VIDIOC_SUBDEV_S_SELECTION</para>
+	</listitem>
+      </varlistentry>
+      <varlistentry>
+	<term><parameter>argp</parameter></term>
+	<listitem>
+	  <para></para>
+	</listitem>
+      </varlistentry>
+    </variablelist>
+  </refsect1>
+
+  <refsect1>
+    <title>Description</title>
+
+    <note>
+      <title>Experimental</title>
+      <para>This is an <link linkend="experimental">experimental</link>
+      interface and may change in the future.</para>
+    </note>
+
+    <para>The selections are used to configure various image
+    processing functionality performed by the subdevs which affect the
+    image size. This currently includes cropping, scaling and
+    composition.</para>
+
+    <para>The selection API replaces <link
+    linkend="vidioc-subdev-g-crop">the old subdev crop API</link>. All
+    the function of the crop API, and more, are supported by the
+    selections API.</para>
+
+    <para>See <xref linkend="subdev"></xref> for
+    more information on how each selection target affects the image
+    processing pipeline inside the subdevice.</para>
+
+    <section>
+      <title>Types of selection targets</title>
+
+      <para>There are two types of selection targets: actual and bounds.
+      The ACTUAL targets are the targets which configure the hardware.
+      The BOUNDS target will return a rectangle that contain all
+      possible ACTUAL rectangles.</para>
+    </section>
+
+    <section>
+      <title>Discovering supported features</title>
+
+      <para>To discover which targets are supported, the user can
+      perform <constant>VIDIOC_SUBDEV_G_SELECTION</constant> on them.
+      Any unsupported target will return
+      <constant>EINVAL</constant>.</para>
+    </section>
+
+    <table pgwide="1" frame="none" id="v4l2-subdev-selection-targets">
+      <title>V4L2 subdev selection targets</title>
+      <tgroup cols="3">
+        &cs-def;
+	<tbody valign="top">
+	  <row>
+	    <entry><constant>V4L2_SUBDEV_SEL_TGT_CROP_ACTUAL</constant></entry>
+	    <entry>0x0000</entry>
+	    <entry>Actual crop. Defines the cropping
+	    performed by the processing step.</entry>
+	  </row>
+	  <row>
+	    <entry><constant>V4L2_SUBDEV_SEL_TGT_CROP_BOUNDS</constant></entry>
+	    <entry>0x0002</entry>
+	    <entry>Bounds of the crop rectangle.</entry>
+	  </row>
+	  <row>
+	    <entry><constant>V4L2_SUBDEV_SEL_TGT_COMPOSE_ACTUAL</constant></entry>
+	    <entry>0x0100</entry>
+	    <entry>Actual compose rectangle. Used to configure scaling
+	    on sink pads and composition on source pads.</entry>
+	  </row>
+	  <row>
+	    <entry><constant>V4L2_SUBDEV_SEL_TGT_COMPOSE_BOUNDS</constant></entry>
+	    <entry>0x0102</entry>
+	    <entry>Bounds of the compose rectangle.</entry>
+	  </row>
+	</tbody>
+      </tgroup>
+    </table>
+
+    <table pgwide="1" frame="none" id="v4l2-subdev-selection-flags">
+      <title>V4L2 subdev selection flags</title>
+      <tgroup cols="3">
+        &cs-def;
+	<tbody valign="top">
+	  <row>
+	    <entry><constant>V4L2_SUBDEV_SEL_FLAG_SIZE_GE</constant></entry>
+	    <entry>(1 &lt;&lt; 0)</entry> <entry>Suggest the driver it
+	    should choose greater or equal rectangle (in size) than
+	    was requested. Albeit the driver may choose a lesser size,
+	    it will only do so due to hardware limitations. Without
+	    this flag (and
+	    <constant>V4L2_SUBDEV_SEL_FLAG_SIZE_LE</constant>) the
+	    behaviour is to choose the closest possible
+	    rectangle.</entry>
+	  </row>
+	  <row>
+	    <entry><constant>V4L2_SUBDEV_SEL_FLAG_SIZE_LE</constant></entry>
+	    <entry>(1 &lt;&lt; 1)</entry> <entry>Suggest the driver it
+	    should choose lesser or equal rectangle (in size) than was
+	    requested. Albeit the driver may choose a greater size, it
+	    will only do so due to hardware limitations.</entry>
+	  </row>
+	  <row>
+	    <entry><constant>V4L2_SUBDEV_SEL_FLAG_KEEP_CONFIG</constant></entry>
+	    <entry>(1 &lt;&lt; 2)</entry>
+	    <entry>The configuration should not be propagated to any
+	    further processing steps. If this flag is not given, the
+	    configuration is propagated inside the subdevice to all
+	    further processing steps.</entry>
+	  </row>
+	</tbody>
+      </tgroup>
+    </table>
+
+    <table pgwide="1" frame="none" id="v4l2-subdev-selection">
+      <title>struct <structname>v4l2_subdev_selection</structname></title>
+      <tgroup cols="3">
+        &cs-str;
+	<tbody valign="top">
+	  <row>
+	    <entry>__u32</entry>
+	    <entry><structfield>which</structfield></entry>
+	    <entry>Active or try selection, from
+	    &v4l2-subdev-format-whence;.</entry>
+	  </row>
+	  <row>
+	    <entry>__u32</entry>
+	    <entry><structfield>pad</structfield></entry>
+	    <entry>Pad number as reported by the media framework.</entry>
+	  </row>
+	  <row>
+	    <entry>__u32</entry>
+	    <entry><structfield>target</structfield></entry>
+	    <entry>Target selection rectangle. See
+	    <xref linkend="v4l2-subdev-selection-targets">.</xref>.</entry>
+	  </row>
+	  <row>
+	    <entry>__u32</entry>
+	    <entry><structfield>flags</structfield></entry>
+	    <entry>Flags. See
+	    <xref linkend="v4l2-subdev-selection-flags">.</xref></entry>
+	  </row>
+	  <row>
+	    <entry>&v4l2-rect;</entry>
+	    <entry><structfield>rect</structfield></entry>
+	    <entry>Selection rectangle, in pixels.</entry>
+	  </row>
+	  <row>
+	    <entry>__u32</entry>
+	    <entry><structfield>reserved</structfield>[8]</entry>
+	    <entry>Reserved for future extensions. Applications and drivers must
+	    set the array to zero.</entry>
+	  </row>
+	</tbody>
+      </tgroup>
+    </table>
+
+  </refsect1>
+
+  <refsect1>
+    &return-value;
+
+    <variablelist>
+      <varlistentry>
+	<term><errorcode>EBUSY</errorcode></term>
+	<listitem>
+	  <para>The selection rectangle can't be changed because the
+	  pad is currently busy. This can be caused, for instance, by
+	  an active video stream on the pad. The ioctl must not be
+	  retried without performing another action to fix the problem
+	  first. Only returned by
+	  <constant>VIDIOC_SUBDEV_S_SELECTION</constant></para>
+	</listitem>
+      </varlistentry>
+      <varlistentry>
+	<term><errorcode>EINVAL</errorcode></term>
+	<listitem>
+	  <para>The &v4l2-subdev-selection;
+	  <structfield>pad</structfield> references a non-existing
+	  pad, the <structfield>which</structfield> field references a
+	  non-existing format, or the selection target is not
+	  supported on the given subdev pad.</para>
+	</listitem>
+      </varlistentry>
+    </variablelist>
+  </refsect1>
+</refentry>