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Diffstat (limited to 'Documentation/DocBook/media/v4l/vidioc-g-fmt.xml')
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diff --git a/Documentation/DocBook/media/v4l/vidioc-g-fmt.xml b/Documentation/DocBook/media/v4l/vidioc-g-fmt.xml new file mode 100644 index 000000000..4fe19a7a9 --- /dev/null +++ b/Documentation/DocBook/media/v4l/vidioc-g-fmt.xml @@ -0,0 +1,204 @@ +<refentry id="vidioc-g-fmt"> + <refmeta> + <refentrytitle>ioctl VIDIOC_G_FMT, VIDIOC_S_FMT, +VIDIOC_TRY_FMT</refentrytitle> + &manvol; + </refmeta> + + <refnamediv> + <refname>VIDIOC_G_FMT</refname> + <refname>VIDIOC_S_FMT</refname> + <refname>VIDIOC_TRY_FMT</refname> + <refpurpose>Get or set the data format, try a format</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_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_G_FMT, VIDIOC_S_FMT, VIDIOC_TRY_FMT</para> + </listitem> + </varlistentry> + <varlistentry> + <term><parameter>argp</parameter></term> + <listitem> + <para></para> + </listitem> + </varlistentry> + </variablelist> + </refsect1> + + <refsect1> + <title>Description</title> + + <para>These ioctls are used to negotiate the format of data +(typically image format) exchanged between driver and +application.</para> + + <para>To query the current parameters applications set the +<structfield>type</structfield> field of a struct +<structname>v4l2_format</structname> to the respective buffer (stream) +type. For example video capture devices use +<constant>V4L2_BUF_TYPE_VIDEO_CAPTURE</constant> or +<constant>V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE</constant>. When the application +calls the <constant>VIDIOC_G_FMT</constant> ioctl with a pointer to +this structure the driver fills the respective member of the +<structfield>fmt</structfield> union. In case of video capture devices +that is either the &v4l2-pix-format; <structfield>pix</structfield> or +the &v4l2-pix-format-mplane; <structfield>pix_mp</structfield> member. +When the requested buffer type is not supported drivers return an +&EINVAL;.</para> + + <para>To change the current format parameters applications +initialize the <structfield>type</structfield> field and all +fields of the respective <structfield>fmt</structfield> +union member. For details see the documentation of the various devices +types in <xref linkend="devices" />. Good practice is to query the +current parameters first, and to +modify only those parameters not suitable for the application. When +the application calls the <constant>VIDIOC_S_FMT</constant> ioctl +with a pointer to a <structname>v4l2_format</structname> structure +the driver checks +and adjusts the parameters against hardware abilities. Drivers +should not return an error code unless the <structfield>type</structfield> field is invalid, this is +a mechanism to fathom device capabilities and to approach parameters +acceptable for both the application and driver. On success the driver +may program the hardware, allocate resources and generally prepare for +data exchange. +Finally the <constant>VIDIOC_S_FMT</constant> ioctl returns the +current format parameters as <constant>VIDIOC_G_FMT</constant> does. +Very simple, inflexible devices may even ignore all input and always +return the default parameters. However all V4L2 devices exchanging +data with the application must implement the +<constant>VIDIOC_G_FMT</constant> and +<constant>VIDIOC_S_FMT</constant> ioctl. When the requested buffer +type is not supported drivers return an &EINVAL; on a +<constant>VIDIOC_S_FMT</constant> attempt. When I/O is already in +progress or the resource is not available for other reasons drivers +return the &EBUSY;.</para> + + <para>The <constant>VIDIOC_TRY_FMT</constant> ioctl is equivalent +to <constant>VIDIOC_S_FMT</constant> with one exception: it does not +change driver state. It can also be called at any time, never +returning <errorcode>EBUSY</errorcode>. This function is provided to +negotiate parameters, to learn about hardware limitations, without +disabling I/O or possibly time consuming hardware preparations. +Although strongly recommended drivers are not required to implement +this ioctl.</para> + + <para>The format as returned by <constant>VIDIOC_TRY_FMT</constant> +must be identical to what <constant>VIDIOC_S_FMT</constant> returns for +the same input or output.</para> + + <table pgwide="1" frame="none" id="v4l2-format"> + <title>struct <structname>v4l2_format</structname></title> + <tgroup cols="4"> + <colspec colname="c1" /> + <colspec colname="c2" /> + <colspec colname="c3" /> + <colspec colname="c4" /> + <tbody valign="top"> + <row> + <entry>__u32</entry> + <entry><structfield>type</structfield></entry> + <entry></entry> + <entry>Type of the data stream, see <xref + linkend="v4l2-buf-type" />.</entry> + </row> + <row> + <entry>union</entry> + <entry><structfield>fmt</structfield></entry> + </row> + <row> + <entry></entry> + <entry>&v4l2-pix-format;</entry> + <entry><structfield>pix</structfield></entry> + <entry>Definition of an image format, see <xref + linkend="pixfmt" />, used by video capture and output +devices.</entry> + </row> + <row> + <entry></entry> + <entry>&v4l2-pix-format-mplane;</entry> + <entry><structfield>pix_mp</structfield></entry> + <entry>Definition of an image format, see <xref + linkend="pixfmt" />, used by video capture and output +devices that support the <link linkend="planar-apis">multi-planar +version of the API</link>.</entry> + </row> + <row> + <entry></entry> + <entry>&v4l2-window;</entry> + <entry><structfield>win</structfield></entry> + <entry>Definition of an overlaid image, see <xref + linkend="overlay" />, used by video overlay devices.</entry> + </row> + <row> + <entry></entry> + <entry>&v4l2-vbi-format;</entry> + <entry><structfield>vbi</structfield></entry> + <entry>Raw VBI capture or output parameters. This is +discussed in more detail in <xref linkend="raw-vbi" />. Used by raw VBI +capture and output devices.</entry> + </row> + <row> + <entry></entry> + <entry>&v4l2-sliced-vbi-format;</entry> + <entry><structfield>sliced</structfield></entry> + <entry>Sliced VBI capture or output parameters. See +<xref linkend="sliced" /> for details. Used by sliced VBI +capture and output devices.</entry> + </row> + <row> + <entry></entry> + <entry>&v4l2-sdr-format;</entry> + <entry><structfield>sdr</structfield></entry> + <entry>Definition of a data format, see +<xref linkend="pixfmt" />, used by SDR capture devices.</entry> + </row> + <row> + <entry></entry> + <entry>__u8</entry> + <entry><structfield>raw_data</structfield>[200]</entry> + <entry>Place holder for future extensions.</entry> + </row> + </tbody> + </tgroup> + </table> + </refsect1> + + <refsect1> + &return-value; + + <variablelist> + <varlistentry> + <term><errorcode>EINVAL</errorcode></term> + <listitem> + <para>The &v4l2-format; <structfield>type</structfield> +field is invalid or the requested buffer type not supported.</para> + </listitem> + </varlistentry> + </variablelist> + </refsect1> +</refentry> |