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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>