184 lines
6.4 KiB
XML
184 lines
6.4 KiB
XML
<refentry id="vidioc-subdev-g-fmt">
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<refmeta>
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<refentrytitle>ioctl VIDIOC_SUBDEV_G_FMT, VIDIOC_SUBDEV_S_FMT</refentrytitle>
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&manvol;
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</refmeta>
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<refnamediv>
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<refname>VIDIOC_SUBDEV_G_FMT</refname>
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<refname>VIDIOC_SUBDEV_S_FMT</refname>
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<refpurpose>Get or set the data format on a subdev pad</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<funcsynopsis>
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<funcprototype>
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<funcdef>int <function>ioctl</function></funcdef>
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<paramdef>int <parameter>fd</parameter></paramdef>
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<paramdef>int <parameter>request</parameter></paramdef>
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<paramdef>struct v4l2_subdev_format *<parameter>argp</parameter>
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</paramdef>
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</funcprototype>
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</funcsynopsis>
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</refsynopsisdiv>
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<refsect1>
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<title>Arguments</title>
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<variablelist>
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<varlistentry>
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<term><parameter>fd</parameter></term>
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<listitem>
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<para>&fd;</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>request</parameter></term>
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<listitem>
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<para>VIDIOC_SUBDEV_G_FMT, VIDIOC_SUBDEV_S_FMT</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>argp</parameter></term>
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<listitem>
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<para></para>
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</listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<refsect1>
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<title>Description</title>
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<note>
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<title>Experimental</title>
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<para>This is an <link linkend="experimental">experimental</link>
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interface and may change in the future.</para>
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</note>
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<para>These ioctls are used to negotiate the frame format at specific
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subdev pads in the image pipeline.</para>
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<para>To retrieve the current format applications set the
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<structfield>pad</structfield> field of a &v4l2-subdev-format; to the
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desired pad number as reported by the media API and the
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<structfield>which</structfield> field to
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<constant>V4L2_SUBDEV_FORMAT_ACTIVE</constant>. When they call the
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<constant>VIDIOC_SUBDEV_G_FMT</constant> ioctl with a pointer to this
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structure the driver fills the members of the <structfield>format</structfield>
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field.</para>
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<para>To change the current format applications set both the
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<structfield>pad</structfield> and <structfield>which</structfield> fields
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and all members of the <structfield>format</structfield> field. When they
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call the <constant>VIDIOC_SUBDEV_S_FMT</constant> ioctl with a pointer to this
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structure the driver verifies the requested format, adjusts it based on the
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hardware capabilities and configures the device. Upon return the
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&v4l2-subdev-format; contains the current format as would be returned by a
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<constant>VIDIOC_SUBDEV_G_FMT</constant> call.</para>
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<para>Applications can query the device capabilities by setting the
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<structfield>which</structfield> to
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<constant>V4L2_SUBDEV_FORMAT_TRY</constant>. When set, 'try' formats are not
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applied to the device by the driver, but are changed exactly as active
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formats and stored in the sub-device file handle. Two applications querying
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the same sub-device would thus not interact with each other.</para>
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<para>For instance, to try a format at the output pad of a sub-device,
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applications would first set the try format at the sub-device input with the
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<constant>VIDIOC_SUBDEV_S_FMT</constant> ioctl. They would then either
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retrieve the default format at the output pad with the
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<constant>VIDIOC_SUBDEV_G_FMT</constant> ioctl, or set the desired output
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pad format with the <constant>VIDIOC_SUBDEV_S_FMT</constant> ioctl and check
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the returned value.</para>
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<para>Try formats do not depend on active formats, but can depend on the
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current links configuration or sub-device controls value. For instance, a
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low-pass noise filter might crop pixels at the frame boundaries, modifying
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its output frame size.</para>
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<para>Drivers must not return an error solely because the requested format
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doesn't match the device capabilities. They must instead modify the format
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to match what the hardware can provide. The modified format should be as
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close as possible to the original request.</para>
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<table pgwide="1" frame="none" id="v4l2-subdev-format">
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<title>struct <structname>v4l2_subdev_format</structname></title>
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<tgroup cols="3">
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&cs-str;
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<tbody valign="top">
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<row>
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<entry>__u32</entry>
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<entry><structfield>pad</structfield></entry>
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<entry>Pad number as reported by the media controller API.</entry>
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</row>
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<row>
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<entry>__u32</entry>
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<entry><structfield>which</structfield></entry>
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<entry>Format to modified, from &v4l2-subdev-format-whence;.</entry>
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</row>
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<row>
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<entry>&v4l2-mbus-framefmt;</entry>
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<entry><structfield>format</structfield></entry>
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<entry>Definition of an image format, see <xref
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linkend="v4l2-mbus-framefmt" /> for details.</entry>
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</row>
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<row>
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<entry>__u32</entry>
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<entry><structfield>reserved</structfield>[8]</entry>
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<entry>Reserved for future extensions. Applications and drivers must
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set the array to zero.</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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<table pgwide="1" frame="none" id="v4l2-subdev-format-whence">
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<title>enum <structname>v4l2_subdev_format_whence</structname></title>
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<tgroup cols="3">
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&cs-def;
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<tbody valign="top">
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<row>
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<entry>V4L2_SUBDEV_FORMAT_TRY</entry>
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<entry>0</entry>
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<entry>Try formats, used for querying device capabilities.</entry>
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</row>
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<row>
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<entry>V4L2_SUBDEV_FORMAT_ACTIVE</entry>
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<entry>1</entry>
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<entry>Active formats, applied to the hardware.</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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</refsect1>
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<refsect1>
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&return-value;
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<variablelist>
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<varlistentry>
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<term><errorcode>EBUSY</errorcode></term>
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<listitem>
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<para>The format can't be changed because the pad is currently busy.
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This can be caused, for instance, by an active video stream on the
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pad. The ioctl must not be retried without performing another action
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to fix the problem first. Only returned by
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<constant>VIDIOC_SUBDEV_S_FMT</constant></para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><errorcode>EINVAL</errorcode></term>
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<listitem>
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<para>The &v4l2-subdev-format; <structfield>pad</structfield>
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references a non-existing pad, or the <structfield>which</structfield>
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field references a non-existing format.</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<refsect1>
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&return-value;
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</refsect1>
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</refentry>
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