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Diffstat (limited to 'Documentation/DocBook/v4l/vidioc-subdev-g-fmt.xml')
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diff --git a/Documentation/DocBook/v4l/vidioc-subdev-g-fmt.xml b/Documentation/DocBook/v4l/vidioc-subdev-g-fmt.xml new file mode 100644 index 0000000..f367c57 --- /dev/null +++ b/Documentation/DocBook/v4l/vidioc-subdev-g-fmt.xml @@ -0,0 +1,180 @@ +<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> +</refentry> |