[media] DocBook: Move all media docbook stuff into its own directory

[cascardo/linux.git] / Documentation / DocBook / media / v4l / vidioc-subdev-g-frame-interval.xml

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+<refentry id="vidioc-subdev-g-frame-interval">
+  <refmeta>
+    <refentrytitle>ioctl VIDIOC_SUBDEV_G_FRAME_INTERVAL, VIDIOC_SUBDEV_S_FRAME_INTERVAL</refentrytitle>
+    &manvol;
+  </refmeta>
+
+  <refnamediv>
+    <refname>VIDIOC_SUBDEV_G_FRAME_INTERVAL</refname>
+    <refname>VIDIOC_SUBDEV_S_FRAME_INTERVAL</refname>
+    <refpurpose>Get or set the frame interval 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_frame_interval *<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_FRAME_INTERVAL, VIDIOC_SUBDEV_S_FRAME_INTERVAL</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>These ioctls are used to get and set the frame interval at specific
+    subdev pads in the image pipeline. The frame interval only makes sense for
+    sub-devices that can control the frame period on their own. This includes,
+    for instance, image sensors and TV tuners. Sub-devices that don't support
+    frame intervals must not implement these ioctls.</para>
+
+    <para>To retrieve the current frame interval applications set the
+    <structfield>pad</structfield> field of a &v4l2-subdev-frame-interval; to
+    the desired pad number as reported by the media controller API. When they
+    call the <constant>VIDIOC_SUBDEV_G_FRAME_INTERVAL</constant> ioctl with a
+    pointer to this structure the driver fills the members of the
+    <structfield>interval</structfield> field.</para>
+
+    <para>To change the current frame interval applications set both the
+    <structfield>pad</structfield> field and all members of the
+    <structfield>interval</structfield> field. When they call the
+    <constant>VIDIOC_SUBDEV_S_FRAME_INTERVAL</constant> ioctl with a pointer to
+    this structure the driver verifies the requested interval, adjusts it based
+    on the hardware capabilities and configures the device. Upon return the
+    &v4l2-subdev-frame-interval; contains the current frame interval as would be
+    returned by a <constant>VIDIOC_SUBDEV_G_FRAME_INTERVAL</constant> call.
+    </para>
+
+    <para>Drivers must not return an error solely because the requested interval
+    doesn't match the device capabilities. They must instead modify the interval
+    to match what the hardware can provide. The modified interval should be as
+    close as possible to the original request.</para>
+
+    <para>Sub-devices that support the frame interval ioctls should implement
+    them on a single pad only. Their behaviour when supported on multiple pads
+    of the same sub-device is not defined.</para>
+
+    <table pgwide="1" frame="none" id="v4l2-subdev-frame-interval">
+      <title>struct <structname>v4l2_subdev_frame_interval</structname></title>
+      <tgroup cols="3">
+        &cs-str;
+       <tbody valign="top">
+         <row>
+           <entry>__u32</entry>
+           <entry><structfield>pad</structfield></entry>
+           <entry>Pad number as reported by the media controller API.</entry>
+         </row>
+         <row>
+           <entry>&v4l2-fract;</entry>
+           <entry><structfield>interval</structfield></entry>
+           <entry>Period, in seconds, between consecutive video frames.</entry>
+         </row>
+         <row>
+           <entry>__u32</entry>
+           <entry><structfield>reserved</structfield>[9]</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 frame interval 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_FRAME_INTERVAL</constant></para>
+       </listitem>
+      </varlistentry>
+      <varlistentry>
+       <term><errorcode>EINVAL</errorcode></term>
+       <listitem>
+         <para>The &v4l2-subdev-frame-interval; <structfield>pad</structfield>
+         references a non-existing pad, or the pad doesn't support frame
+         intervals.</para>
+       </listitem>
+      </varlistentry>
+    </variablelist>
+  </refsect1>
+</refentry>