Documentation/DocBook/v4l/vidioc-g-parm.xml - kernel/msm-4.9 - Gitiles

 <refentry id="vidioc-g-parm">
   <refmeta>
     <refentrytitle>ioctl VIDIOC_G_PARM, VIDIOC_S_PARM</refentrytitle>
     &manvol;
   </refmeta>

   <refnamediv>
     <refname>VIDIOC_G_PARM</refname>
     <refname>VIDIOC_S_PARM</refname>
     <refpurpose>Get or set streaming parameters</refpurpose>
   </refnamediv>

   <refsynopsisdiv>
     <funcsynopsis>
       <funcprototype>
 	<funcdef>int <function>ioctl</function></funcdef>
 	<paramdef>int <parameter>fd</parameter></paramdef>
 	<paramdef>int <parameter>request</parameter></paramdef>
 	<paramdef>v4l2_streamparm *<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_PARM, VIDIOC_S_PARM</para>
 	</listitem>
       </varlistentry>
       <varlistentry>
 	<term><parameter>argp</parameter></term>
 	<listitem>
 	  <para></para>
 	</listitem>
       </varlistentry>
     </variablelist>
   </refsect1>

   <refsect1>
     <title>Description</title>

     <para>The current video standard determines a nominal number of
 frames per second. If less than this number of frames is to be
 captured or output, applications can request frame skipping or
 duplicating on the driver side. This is especially useful when using
 the <function>read()</function> or <function>write()</function>, which
 are not augmented by timestamps or sequence counters, and to avoid
 unneccessary data copying.</para>

     <para>Further these ioctls can be used to determine the number of
 buffers used internally by a driver in read/write mode. For
 implications see the section discussing the &func-read;
 function.</para>

     <para>To get and set the streaming parameters applications call
 the <constant>VIDIOC_G_PARM</constant> and
 <constant>VIDIOC_S_PARM</constant> ioctl, respectively. They take a
 pointer to a struct <structname>v4l2_streamparm</structname> which
 contains a union holding separate parameters for input and output
 devices.</para>

     <table pgwide="1" frame="none" id="v4l2-streamparm">
       <title>struct <structname>v4l2_streamparm</structname></title>
       <tgroup cols="4">
 	&cs-ustr;
 	<tbody valign="top">
 	  <row>
 	    <entry>&v4l2-buf-type;</entry>
 	    <entry><structfield>type</structfield></entry>
 	    <entry></entry>
 	    <entry>The buffer (stream) type, same as &v4l2-format;
 <structfield>type</structfield>, set by the application.</entry>
 	  </row>
 	  <row>
 	    <entry>union</entry>
 	    <entry><structfield>parm</structfield></entry>
 	    <entry></entry>
 	    <entry></entry>
 	  </row>
 	  <row>
 	    <entry></entry>
 	    <entry>&v4l2-captureparm;</entry>
 	    <entry><structfield>capture</structfield></entry>
 	    <entry>Parameters for capture devices, used when
 <structfield>type</structfield> is
 <constant>V4L2_BUF_TYPE_VIDEO_CAPTURE</constant>.</entry>
 	  </row>
 	  <row>
 	    <entry></entry>
 	    <entry>&v4l2-outputparm;</entry>
 	    <entry><structfield>output</structfield></entry>
 	    <entry>Parameters for output devices, used when
 <structfield>type</structfield> is
 <constant>V4L2_BUF_TYPE_VIDEO_OUTPUT</constant>.</entry>
 	  </row>
 	  <row>
 	    <entry></entry>
 	    <entry>__u8</entry>
 	    <entry><structfield>raw_data</structfield>[200]</entry>
 	    <entry>A place holder for future extensions and custom
 (driver defined) buffer types <constant>V4L2_BUF_TYPE_PRIVATE</constant> and
 higher.</entry>
 	  </row>
 	</tbody>
       </tgroup>
     </table>

     <table pgwide="1" frame="none" id="v4l2-captureparm">
       <title>struct <structname>v4l2_captureparm</structname></title>
       <tgroup cols="3">
 	&cs-str;
 	<tbody valign="top">
 	  <row>
 	    <entry>__u32</entry>
 	    <entry><structfield>capability</structfield></entry>
 	    <entry>See <xref linkend="parm-caps" />.</entry>
 	  </row>
 	  <row>
 	    <entry>__u32</entry>
 	    <entry><structfield>capturemode</structfield></entry>
 	    <entry>Set by drivers and applications, see <xref linkend="parm-flags" />.</entry>
 	  </row>
 	  <row>
 	    <entry>&v4l2-fract;</entry>
 	    <entry><structfield>timeperframe</structfield></entry>
 	    <entry><para>This is is the desired period between
 successive frames captured by the driver, in seconds. The
 field is intended to skip frames on the driver side, saving I/O
 bandwidth.</para><para>Applications store here the desired frame
 period, drivers return the actual frame period, which must be greater
 or equal to the nominal frame period determined by the current video
 standard (&v4l2-standard; <structfield>frameperiod</structfield>
 field). Changing the video standard (also implicitly by switching the
 video input) may reset this parameter to the nominal frame period. To
 reset manually applications can just set this field to
 zero.</para><para>Drivers support this function only when they set the
 <constant>V4L2_CAP_TIMEPERFRAME</constant> flag in the
 <structfield>capability</structfield> field.</para></entry>
 	  </row>
 	  <row>
 	    <entry>__u32</entry>
 	    <entry><structfield>extendedmode</structfield></entry>
 	    <entry>Custom (driver specific) streaming parameters. When
 unused, applications and drivers must set this field to zero.
 Applications using this field should check the driver name and
 version, see <xref linkend="querycap" />.</entry>
 	  </row>
 	  <row>
 	    <entry>__u32</entry>
 	    <entry><structfield>readbuffers</structfield></entry>
 	    <entry>Applications set this field to the desired number
 of buffers used internally by the driver in &func-read; mode. Drivers
 return the actual number of buffers. When an application requests zero
 buffers, drivers should just return the current setting rather than
 the minimum or an error code. For details see <xref
 		linkend="rw" />.</entry>
 	  </row>
 	  <row>
 	    <entry>__u32</entry>
 	    <entry><structfield>reserved</structfield>[4]</entry>
 	    <entry>Reserved for future extensions. Drivers and
 applications must set the array to zero.</entry>
 	  </row>
 	</tbody>
       </tgroup>
     </table>

     <table pgwide="1" frame="none" id="v4l2-outputparm">
       <title>struct <structname>v4l2_outputparm</structname></title>
       <tgroup cols="3">
 	&cs-str;
 	<tbody valign="top">
 	  <row>
 	    <entry>__u32</entry>
 	    <entry><structfield>capability</structfield></entry>
 	    <entry>See <xref linkend="parm-caps" />.</entry>
 	  </row>
 	  <row>
 	    <entry>__u32</entry>
 	    <entry><structfield>outputmode</structfield></entry>
 	    <entry>Set by drivers and applications, see <xref
 	    linkend="parm-flags" />.</entry>
 	  </row>
 	  <row>
 	    <entry>&v4l2-fract;</entry>
 	    <entry><structfield>timeperframe</structfield></entry>
 	    <entry>This is is the desired period between
 successive frames output by the driver, in seconds.</entry>
 	  </row>
 	  <row>
 	    <entry spanname="hspan"><para>The field is intended to
 repeat frames on the driver side in &func-write; mode (in streaming
 mode timestamps can be used to throttle the output), saving I/O
 bandwidth.</para><para>Applications store here the desired frame
 period, drivers return the actual frame period, which must be greater
 or equal to the nominal frame period determined by the current video
 standard (&v4l2-standard; <structfield>frameperiod</structfield>
 field). Changing the video standard (also implicitly by switching the
 video output) may reset this parameter to the nominal frame period. To
 reset manually applications can just set this field to
 zero.</para><para>Drivers support this function only when they set the
 <constant>V4L2_CAP_TIMEPERFRAME</constant> flag in the
 <structfield>capability</structfield> field.</para></entry>
 	  </row>
 	  <row>
 	    <entry>__u32</entry>
 	    <entry><structfield>extendedmode</structfield></entry>
 	    <entry>Custom (driver specific) streaming parameters. When
 unused, applications and drivers must set this field to zero.
 Applications using this field should check the driver name and
 version, see <xref linkend="querycap" />.</entry>
 	  </row>
 	  <row>
 	    <entry>__u32</entry>
 	    <entry><structfield>writebuffers</structfield></entry>
 	    <entry>Applications set this field to the desired number
 of buffers used internally by the driver in
 <function>write()</function> mode. Drivers return the actual number of
 buffers. When an application requests zero buffers, drivers should
 just return the current setting rather than the minimum or an error
 code. For details see <xref linkend="rw" />.</entry>
 	  </row>
 	  <row>
 	    <entry>__u32</entry>
 	    <entry><structfield>reserved</structfield>[4]</entry>
 	    <entry>Reserved for future extensions. Drivers and
 applications must set the array to zero.</entry>
 	  </row>
 	</tbody>
       </tgroup>
     </table>

     <table pgwide="1" frame="none" id="parm-caps">
       <title>Streaming Parameters Capabilites</title>
       <tgroup cols="3">
 	&cs-def;
 	<tbody valign="top">
 	  <row>
 	    <entry><constant>V4L2_CAP_TIMEPERFRAME</constant></entry>
 	    <entry>0x1000</entry>
 	    <entry>The frame skipping/repeating controlled by the
 <structfield>timeperframe</structfield> field is supported.</entry>
 	  </row>
 	</tbody>
       </tgroup>
     </table>

     <table pgwide="1" frame="none" id="parm-flags">
       <title>Capture Parameters Flags</title>
       <tgroup cols="3">
 	&cs-def;
 	<tbody valign="top">
 	  <row>
 	    <entry><constant>V4L2_MODE_HIGHQUALITY</constant></entry>
 	    <entry>0x0001</entry>
 	    <entry><para>High quality imaging mode. High quality mode
 is intended for still imaging applications. The idea is to get the
 best possible image quality that the hardware can deliver. It is not
 defined how the driver writer may achieve that; it will depend on the
 hardware and the ingenuity of the driver writer. High quality mode is
 a different mode from the the regular motion video capture modes. In
 high quality mode:<itemizedlist>
 		  <listitem>
 		    <para>The driver may be able to capture higher
 resolutions than for motion capture.</para>
 		  </listitem>
 		  <listitem>
 		    <para>The driver may support fewer pixel formats
 than motion capture (eg; true color).</para>
 		  </listitem>
 		  <listitem>
 		    <para>The driver may capture and arithmetically
 combine multiple successive fields or frames to remove color edge
 artifacts and reduce the noise in the video data.
 </para>
 		  </listitem>
 		  <listitem>
 		    <para>The driver may capture images in slices like
 a scanner in order to handle larger format images than would otherwise
 be possible. </para>
 		  </listitem>
 		  <listitem>
 		    <para>An image capture operation may be
 significantly slower than motion capture. </para>
 		  </listitem>
 		  <listitem>
 		    <para>Moving objects in the image might have
 excessive motion blur. </para>
 		  </listitem>
 		  <listitem>
 		    <para>Capture might only work through the
 <function>read()</function> call.</para>
 		  </listitem>
 		</itemizedlist></para></entry>
 	  </row>
 	</tbody>
       </tgroup>
     </table>

   </refsect1>

   <refsect1>
     &return-value;

     <variablelist>
       <varlistentry>
 	<term><errorcode>EINVAL</errorcode></term>
 	<listitem>
 	  <para>This ioctl is not supported.</para>
 	</listitem>
       </varlistentry>
     </variablelist>
   </refsect1>
 </refentry>

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	<refentry id="vidioc-g-parm">
	<refmeta>
	<refentrytitle>ioctl VIDIOC_G_PARM, VIDIOC_S_PARM</refentrytitle>
	&manvol;
	</refmeta>

	<refnamediv>
	<refname>VIDIOC_G_PARM</refname>
	<refname>VIDIOC_S_PARM</refname>
	<refpurpose>Get or set streaming parameters</refpurpose>
	</refnamediv>

	<refsynopsisdiv>
	<funcsynopsis>
	<funcprototype>
	<funcdef>int <function>ioctl</function></funcdef>
	<paramdef>int <parameter>fd</parameter></paramdef>
	<paramdef>int <parameter>request</parameter></paramdef>
	<paramdef>v4l2_streamparm *<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_PARM, VIDIOC_S_PARM</para>
	</listitem>
	</varlistentry>
	<varlistentry>
	<term><parameter>argp</parameter></term>
	<listitem>
	<para></para>
	</listitem>
	</varlistentry>
	</variablelist>
	</refsect1>

	<refsect1>
	<title>Description</title>

	<para>The current video standard determines a nominal number of
	frames per second. If less than this number of frames is to be
	captured or output, applications can request frame skipping or
	duplicating on the driver side. This is especially useful when using
	the <function>read()</function> or <function>write()</function>, which
	are not augmented by timestamps or sequence counters, and to avoid
	unneccessary data copying.</para>

	<para>Further these ioctls can be used to determine the number of
	buffers used internally by a driver in read/write mode. For
	implications see the section discussing the &func-read;
	function.</para>

	<para>To get and set the streaming parameters applications call
	the <constant>VIDIOC_G_PARM</constant> and
	<constant>VIDIOC_S_PARM</constant> ioctl, respectively. They take a
	pointer to a struct <structname>v4l2_streamparm</structname> which
	contains a union holding separate parameters for input and output
	devices.</para>

	<table pgwide="1" frame="none" id="v4l2-streamparm">
	<title>struct <structname>v4l2_streamparm</structname></title>
	<tgroup cols="4">
	&cs-ustr;
	<tbody valign="top">
	<row>
	<entry>&v4l2-buf-type;</entry>
	<entry><structfield>type</structfield></entry>
	<entry></entry>
	<entry>The buffer (stream) type, same as &v4l2-format;
	<structfield>type</structfield>, set by the application.</entry>
	</row>
	<row>
	<entry>union</entry>
	<entry><structfield>parm</structfield></entry>
	<entry></entry>
	<entry></entry>
	</row>
	<row>
	<entry></entry>
	<entry>&v4l2-captureparm;</entry>
	<entry><structfield>capture</structfield></entry>
	<entry>Parameters for capture devices, used when
	<structfield>type</structfield> is
	<constant>V4L2_BUF_TYPE_VIDEO_CAPTURE</constant>.</entry>
	</row>
	<row>
	<entry></entry>
	<entry>&v4l2-outputparm;</entry>
	<entry><structfield>output</structfield></entry>
	<entry>Parameters for output devices, used when
	<structfield>type</structfield> is
	<constant>V4L2_BUF_TYPE_VIDEO_OUTPUT</constant>.</entry>
	</row>
	<row>
	<entry></entry>
	<entry>__u8</entry>
	<entry><structfield>raw_data</structfield>[200]</entry>
	<entry>A place holder for future extensions and custom
	(driver defined) buffer types <constant>V4L2_BUF_TYPE_PRIVATE</constant> and
	higher.</entry>
	</row>
	</tbody>
	</tgroup>
	</table>

	<table pgwide="1" frame="none" id="v4l2-captureparm">
	<title>struct <structname>v4l2_captureparm</structname></title>
	<tgroup cols="3">
	&cs-str;
	<tbody valign="top">
	<row>
	<entry>__u32</entry>
	<entry><structfield>capability</structfield></entry>
	<entry>See <xref linkend="parm-caps" />.</entry>
	</row>
	<row>
	<entry>__u32</entry>
	<entry><structfield>capturemode</structfield></entry>
	<entry>Set by drivers and applications, see <xref linkend="parm-flags" />.</entry>
	</row>
	<row>
	<entry>&v4l2-fract;</entry>
	<entry><structfield>timeperframe</structfield></entry>
	<entry><para>This is is the desired period between
	successive frames captured by the driver, in seconds. The
	field is intended to skip frames on the driver side, saving I/O
	bandwidth.</para><para>Applications store here the desired frame
	period, drivers return the actual frame period, which must be greater
	or equal to the nominal frame period determined by the current video
	standard (&v4l2-standard; <structfield>frameperiod</structfield>
	field). Changing the video standard (also implicitly by switching the
	video input) may reset this parameter to the nominal frame period. To
	reset manually applications can just set this field to
	zero.</para><para>Drivers support this function only when they set the
	<constant>V4L2_CAP_TIMEPERFRAME</constant> flag in the
	<structfield>capability</structfield> field.</para></entry>
	</row>
	<row>
	<entry>__u32</entry>
	<entry><structfield>extendedmode</structfield></entry>
	<entry>Custom (driver specific) streaming parameters. When
	unused, applications and drivers must set this field to zero.
	Applications using this field should check the driver name and
	version, see <xref linkend="querycap" />.</entry>
	</row>
	<row>
	<entry>__u32</entry>
	<entry><structfield>readbuffers</structfield></entry>
	<entry>Applications set this field to the desired number
	of buffers used internally by the driver in &func-read; mode. Drivers
	return the actual number of buffers. When an application requests zero
	buffers, drivers should just return the current setting rather than
	the minimum or an error code. For details see <xref
	linkend="rw" />.</entry>
	</row>
	<row>
	<entry>__u32</entry>
	<entry><structfield>reserved</structfield>[4]</entry>
	<entry>Reserved for future extensions. Drivers and
	applications must set the array to zero.</entry>
	</row>
	</tbody>
	</tgroup>
	</table>

	<table pgwide="1" frame="none" id="v4l2-outputparm">
	<title>struct <structname>v4l2_outputparm</structname></title>
	<tgroup cols="3">
	&cs-str;
	<tbody valign="top">
	<row>
	<entry>__u32</entry>
	<entry><structfield>capability</structfield></entry>
	<entry>See <xref linkend="parm-caps" />.</entry>
	</row>
	<row>
	<entry>__u32</entry>
	<entry><structfield>outputmode</structfield></entry>
	<entry>Set by drivers and applications, see <xref
	linkend="parm-flags" />.</entry>
	</row>
	<row>
	<entry>&v4l2-fract;</entry>
	<entry><structfield>timeperframe</structfield></entry>
	<entry>This is is the desired period between
	successive frames output by the driver, in seconds.</entry>
	</row>
	<row>
	<entry spanname="hspan"><para>The field is intended to
	repeat frames on the driver side in &func-write; mode (in streaming
	mode timestamps can be used to throttle the output), saving I/O
	bandwidth.</para><para>Applications store here the desired frame
	period, drivers return the actual frame period, which must be greater
	or equal to the nominal frame period determined by the current video
	standard (&v4l2-standard; <structfield>frameperiod</structfield>
	field). Changing the video standard (also implicitly by switching the
	video output) may reset this parameter to the nominal frame period. To
	reset manually applications can just set this field to
	zero.</para><para>Drivers support this function only when they set the
	<constant>V4L2_CAP_TIMEPERFRAME</constant> flag in the
	<structfield>capability</structfield> field.</para></entry>
	</row>
	<row>
	<entry>__u32</entry>
	<entry><structfield>extendedmode</structfield></entry>
	<entry>Custom (driver specific) streaming parameters. When
	unused, applications and drivers must set this field to zero.
	Applications using this field should check the driver name and
	version, see <xref linkend="querycap" />.</entry>
	</row>
	<row>
	<entry>__u32</entry>
	<entry><structfield>writebuffers</structfield></entry>
	<entry>Applications set this field to the desired number
	of buffers used internally by the driver in
	<function>write()</function> mode. Drivers return the actual number of
	buffers. When an application requests zero buffers, drivers should
	just return the current setting rather than the minimum or an error
	code. For details see <xref linkend="rw" />.</entry>
	</row>
	<row>
	<entry>__u32</entry>
	<entry><structfield>reserved</structfield>[4]</entry>
	<entry>Reserved for future extensions. Drivers and
	applications must set the array to zero.</entry>
	</row>
	</tbody>
	</tgroup>
	</table>

	<table pgwide="1" frame="none" id="parm-caps">
	<title>Streaming Parameters Capabilites</title>
	<tgroup cols="3">
	&cs-def;
	<tbody valign="top">
	<row>
	<entry><constant>V4L2_CAP_TIMEPERFRAME</constant></entry>
	<entry>0x1000</entry>
	<entry>The frame skipping/repeating controlled by the
	<structfield>timeperframe</structfield> field is supported.</entry>
	</row>
	</tbody>
	</tgroup>
	</table>

	<table pgwide="1" frame="none" id="parm-flags">
	<title>Capture Parameters Flags</title>
	<tgroup cols="3">
	&cs-def;
	<tbody valign="top">
	<row>
	<entry><constant>V4L2_MODE_HIGHQUALITY</constant></entry>
	<entry>0x0001</entry>
	<entry><para>High quality imaging mode. High quality mode
	is intended for still imaging applications. The idea is to get the
	best possible image quality that the hardware can deliver. It is not
	defined how the driver writer may achieve that; it will depend on the
	hardware and the ingenuity of the driver writer. High quality mode is
	a different mode from the the regular motion video capture modes. In
	high quality mode:<itemizedlist>
	<listitem>
	<para>The driver may be able to capture higher
	resolutions than for motion capture.</para>
	</listitem>
	<listitem>
	<para>The driver may support fewer pixel formats
	than motion capture (eg; true color).</para>
	</listitem>
	<listitem>
	<para>The driver may capture and arithmetically
	combine multiple successive fields or frames to remove color edge
	artifacts and reduce the noise in the video data.
	</para>
	</listitem>
	<listitem>
	<para>The driver may capture images in slices like
	a scanner in order to handle larger format images than would otherwise
	be possible. </para>
	</listitem>
	<listitem>
	<para>An image capture operation may be
	significantly slower than motion capture. </para>
	</listitem>
	<listitem>
	<para>Moving objects in the image might have
	excessive motion blur. </para>
	</listitem>
	<listitem>
	<para>Capture might only work through the
	<function>read()</function> call.</para>
	</listitem>
	</itemizedlist></para></entry>
	</row>
	</tbody>
	</tgroup>
	</table>

	</refsect1>

	<refsect1>
	&return-value;

	<variablelist>
	<varlistentry>
	<term><errorcode>EINVAL</errorcode></term>
	<listitem>
	<para>This ioctl is not supported.</para>
	</listitem>
	</varlistentry>
	</variablelist>
	</refsect1>
	</refentry>

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