Documentation/DocBook/media/v4l/vidioc-subdev-g-fmt.xml

   1 <refentry id="vidioc-subdev-g-fmt">
   2   <refmeta>
   3     <refentrytitle>ioctl VIDIOC_SUBDEV_G_FMT, VIDIOC_SUBDEV_S_FMT</refentrytitle>
   4     &manvol;
   5   </refmeta>
   6
   7   <refnamediv>
   8     <refname>VIDIOC_SUBDEV_G_FMT</refname>
   9     <refname>VIDIOC_SUBDEV_S_FMT</refname>
  10     <refpurpose>Get or set the data format on a subdev pad</refpurpose>
  11   </refnamediv>
  12
  13   <refsynopsisdiv>
  14     <funcsynopsis>
  15       <funcprototype>
  16         <funcdef>int <function>ioctl</function></funcdef>
  17         <paramdef>int <parameter>fd</parameter></paramdef>
  18         <paramdef>int <parameter>request</parameter></paramdef>
  19         <paramdef>struct v4l2_subdev_format *<parameter>argp</parameter>
  20         </paramdef>
  21       </funcprototype>
  22     </funcsynopsis>
  23   </refsynopsisdiv>
  24
  25   <refsect1>
  26     <title>Arguments</title>
  27
  28     <variablelist>
  29       <varlistentry>
  30         <term><parameter>fd</parameter></term>
  31         <listitem>
  32           <para>&fd;</para>
  33         </listitem>
  34       </varlistentry>
  35       <varlistentry>
  36         <term><parameter>request</parameter></term>
  37         <listitem>
  38           <para>VIDIOC_SUBDEV_G_FMT, VIDIOC_SUBDEV_S_FMT</para>
  39         </listitem>
  40       </varlistentry>
  41       <varlistentry>
  42         <term><parameter>argp</parameter></term>
  43         <listitem>
  44           <para></para>
  45         </listitem>
  46       </varlistentry>
  47     </variablelist>
  48   </refsect1>
  49
  50   <refsect1>
  51     <title>Description</title>
  52
  53     <note>
  54       <title>Experimental</title>
  55       <para>This is an <link linkend="experimental">experimental</link>
  56       interface and may change in the future.</para>
  57     </note>
  58
  59     <para>These ioctls are used to negotiate the frame format at specific
  60     subdev pads in the image pipeline.</para>
  61
  62     <para>To retrieve the current format applications set the
  63     <structfield>pad</structfield> field of a &v4l2-subdev-format; to the
  64     desired pad number as reported by the media API and the
  65     <structfield>which</structfield> field to
  66     <constant>V4L2_SUBDEV_FORMAT_ACTIVE</constant>. When they call the
  67     <constant>VIDIOC_SUBDEV_G_FMT</constant> ioctl with a pointer to this
  68     structure the driver fills the members of the <structfield>format</structfield>
  69     field.</para>
  70
  71     <para>To change the current format applications set both the
  72     <structfield>pad</structfield> and <structfield>which</structfield> fields
  73     and all members of the <structfield>format</structfield> field. When they
  74     call the <constant>VIDIOC_SUBDEV_S_FMT</constant> ioctl with a pointer to this
  75     structure the driver verifies the requested format, adjusts it based on the
  76     hardware capabilities and configures the device. Upon return the
  77     &v4l2-subdev-format; contains the current format as would be returned by a
  78     <constant>VIDIOC_SUBDEV_G_FMT</constant> call.</para>
  79
  80     <para>Applications can query the device capabilities by setting the
  81     <structfield>which</structfield> to
  82     <constant>V4L2_SUBDEV_FORMAT_TRY</constant>. When set, 'try' formats are not
  83     applied to the device by the driver, but are changed exactly as active
  84     formats and stored in the sub-device file handle. Two applications querying
  85     the same sub-device would thus not interact with each other.</para>
  86
  87     <para>For instance, to try a format at the output pad of a sub-device,
  88     applications would first set the try format at the sub-device input with the
  89     <constant>VIDIOC_SUBDEV_S_FMT</constant> ioctl. They would then either
  90     retrieve the default format at the output pad with the
  91     <constant>VIDIOC_SUBDEV_G_FMT</constant> ioctl, or set the desired output
  92     pad format with the <constant>VIDIOC_SUBDEV_S_FMT</constant> ioctl and check
  93     the returned value.</para>
  94
  95     <para>Try formats do not depend on active formats, but can depend on the
  96     current links configuration or sub-device controls value. For instance, a
  97     low-pass noise filter might crop pixels at the frame boundaries, modifying
  98     its output frame size.</para>
  99
 100     <para>Drivers must not return an error solely because the requested format
 101     doesn't match the device capabilities. They must instead modify the format
 102     to match what the hardware can provide. The modified format should be as
 103     close as possible to the original request.</para>
 104
 105     <table pgwide="1" frame="none" id="v4l2-subdev-format">
 106       <title>struct <structname>v4l2_subdev_format</structname></title>
 107       <tgroup cols="3">
 108         &cs-str;
 109         <tbody valign="top">
 110           <row>
 111             <entry>__u32</entry>
 112             <entry><structfield>pad</structfield></entry>
 113             <entry>Pad number as reported by the media controller API.</entry>
 114           </row>
 115           <row>
 116             <entry>__u32</entry>
 117             <entry><structfield>which</structfield></entry>
 118             <entry>Format to modified, from &v4l2-subdev-format-whence;.</entry>
 119           </row>
 120           <row>
 121             <entry>&v4l2-mbus-framefmt;</entry>
 122             <entry><structfield>format</structfield></entry>
 123             <entry>Definition of an image format, see <xref
 124             linkend="v4l2-mbus-framefmt" /> for details.</entry>
 125           </row>
 126           <row>
 127             <entry>__u32</entry>
 128             <entry><structfield>reserved</structfield>[8]</entry>
 129             <entry>Reserved for future extensions. Applications and drivers must
 130             set the array to zero.</entry>
 131           </row>
 132         </tbody>
 133       </tgroup>
 134     </table>
 135
 136     <table pgwide="1" frame="none" id="v4l2-subdev-format-whence">
 137       <title>enum <structname>v4l2_subdev_format_whence</structname></title>
 138       <tgroup cols="3">
 139         &cs-def;
 140         <tbody valign="top">
 141           <row>
 142             <entry>V4L2_SUBDEV_FORMAT_TRY</entry>
 143             <entry>0</entry>
 144             <entry>Try formats, used for querying device capabilities.</entry>
 145           </row>
 146           <row>
 147             <entry>V4L2_SUBDEV_FORMAT_ACTIVE</entry>
 148             <entry>1</entry>
 149             <entry>Active formats, applied to the hardware.</entry>
 150           </row>
 151         </tbody>
 152       </tgroup>
 153     </table>
 154   </refsect1>
 155
 156   <refsect1>
 157     &return-value;
 158
 159     <variablelist>
 160       <varlistentry>
 161         <term><errorcode>EBUSY</errorcode></term>
 162         <listitem>
 163           <para>The format can't be changed because the pad is currently busy.
 164           This can be caused, for instance, by an active video stream on the
 165           pad. The ioctl must not be retried without performing another action
 166           to fix the problem first. Only returned by
 167           <constant>VIDIOC_SUBDEV_S_FMT</constant></para>
 168         </listitem>
 169       </varlistentry>
 170       <varlistentry>
 171         <term><errorcode>EINVAL</errorcode></term>
 172         <listitem>
 173           <para>The &v4l2-subdev-format; <structfield>pad</structfield>
 174           references a non-existing pad, or the <structfield>which</structfield>
 175           field references a non-existing format.</para>
 176         </listitem>
 177       </varlistentry>
 178     </variablelist>
 179   </refsect1>
 180 </refentry>