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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>
|
