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+<refentry id="vidioc-subdev-g-fmt">
+ <refmeta>
+ <refentrytitle>ioctl VIDIOC_SUBDEV_G_FMT, VIDIOC_SUBDEV_S_FMT</refentrytitle>
+ &manvol;
+ </refmeta>
+
+ <refnamediv>
+ <refname>VIDIOC_SUBDEV_G_FMT</refname>
+ <refname>VIDIOC_SUBDEV_S_FMT</refname>
+ <refpurpose>Get or set the data format 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_format *<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_FMT, VIDIOC_SUBDEV_S_FMT</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 negotiate the frame format at specific
+ subdev pads in the image pipeline.</para>
+
+ <para>To retrieve the current format applications set the
+ <structfield>pad</structfield> field of a &v4l2-subdev-format; to the
+ desired pad number as reported by the media API and the
+ <structfield>which</structfield> field to
+ <constant>V4L2_SUBDEV_FORMAT_ACTIVE</constant>. When they call the
+ <constant>VIDIOC_SUBDEV_G_FMT</constant> ioctl with a pointer to this
+ structure the driver fills the members of the <structfield>format</structfield>
+ field.</para>
+
+ <para>To change the current format applications set both the
+ <structfield>pad</structfield> and <structfield>which</structfield> fields
+ and all members of the <structfield>format</structfield> field. When they
+ call the <constant>VIDIOC_SUBDEV_S_FMT</constant> ioctl with a pointer to this
+ structure the driver verifies the requested format, adjusts it based on the
+ hardware capabilities and configures the device. Upon return the
+ &v4l2-subdev-format; contains the current format as would be returned by a
+ <constant>VIDIOC_SUBDEV_G_FMT</constant> call.</para>
+
+ <para>Applications can query the device capabilities by setting the
+ <structfield>which</structfield> to
+ <constant>V4L2_SUBDEV_FORMAT_TRY</constant>. When set, 'try' formats are not
+ applied to the device by the driver, but are changed exactly as active
+ formats and stored in the sub-device file handle. Two applications querying
+ the same sub-device would thus not interact with each other.</para>
+
+ <para>For instance, to try a format at the output pad of a sub-device,
+ applications would first set the try format at the sub-device input with the
+ <constant>VIDIOC_SUBDEV_S_FMT</constant> ioctl. They would then either
+ retrieve the default format at the output pad with the
+ <constant>VIDIOC_SUBDEV_G_FMT</constant> ioctl, or set the desired output
+ pad format with the <constant>VIDIOC_SUBDEV_S_FMT</constant> ioctl and check
+ the returned value.</para>
+
+ <para>Try formats do not depend on active formats, but can depend on the
+ current links configuration or sub-device controls value. For instance, a
+ low-pass noise filter might crop pixels at the frame boundaries, modifying
+ its output frame size.</para>
+
+ <para>Drivers must not return an error solely because the requested format
+ doesn't match the device capabilities. They must instead modify the format
+ to match what the hardware can provide. The modified format should be as
+ close as possible to the original request.</para>
+
+ <table pgwide="1" frame="none" id="v4l2-subdev-format">
+ <title>struct <structname>v4l2_subdev_format</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>__u32</entry>
+ <entry><structfield>which</structfield></entry>
+ <entry>Format to modified, from &v4l2-subdev-format-whence;.</entry>
+ </row>
+ <row>
+ <entry>&v4l2-mbus-framefmt;</entry>
+ <entry><structfield>format</structfield></entry>
+ <entry>Definition of an image format, see <xref
+ linkend="v4l2-mbus-framefmt" /> for details.</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>
+
+ <table pgwide="1" frame="none" id="v4l2-subdev-format-whence">
+ <title>enum <structname>v4l2_subdev_format_whence</structname></title>
+ <tgroup cols="3">
+ &cs-def;
+ <tbody valign="top">
+ <row>
+ <entry>V4L2_SUBDEV_FORMAT_TRY</entry>
+ <entry>0</entry>
+ <entry>Try formats, used for querying device capabilities.</entry>
+ </row>
+ <row>
+ <entry>V4L2_SUBDEV_FORMAT_ACTIVE</entry>
+ <entry>1</entry>
+ <entry>Active formats, applied to the hardware.</entry>
+ </row>
+ </tbody>
+ </tgroup>
+ </table>
+ </refsect1>
+
+ <refsect1>
+ &return-value;
+
+ <variablelist>
+ <varlistentry>
+ <term><errorcode>EBUSY</errorcode></term>
+ <listitem>
+ <para>The format 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_FMT</constant></para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><errorcode>EINVAL</errorcode></term>
+ <listitem>
+ <para>The &v4l2-subdev-format; <structfield>pad</structfield>
+ references a non-existing pad, or the <structfield>which</structfield>
+ field references a non-existing format.</para>
+ </listitem>
+ </varlistentry>
+ </variablelist>
+ </refsect1>
+ <refsect1>
+ &return-value;
+ </refsect1>
+</refentry>