Based on kernel version 4.7.2. Page generated on 2016-08-22 22:45 EST.
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 <para>These ioctls are used to negotiate the frame format at specific 54 subdev pads in the image pipeline.</para> 55 56 <para>To retrieve the current format applications set the 57 <structfield>pad</structfield> field of a &v4l2-subdev-format; to the 58 desired pad number as reported by the media API and the 59 <structfield>which</structfield> field to 60 <constant>V4L2_SUBDEV_FORMAT_ACTIVE</constant>. When they call the 61 <constant>VIDIOC_SUBDEV_G_FMT</constant> ioctl with a pointer to this 62 structure the driver fills the members of the <structfield>format</structfield> 63 field.</para> 64 65 <para>To change the current format applications set both the 66 <structfield>pad</structfield> and <structfield>which</structfield> fields 67 and all members of the <structfield>format</structfield> field. When they 68 call the <constant>VIDIOC_SUBDEV_S_FMT</constant> ioctl with a pointer to this 69 structure the driver verifies the requested format, adjusts it based on the 70 hardware capabilities and configures the device. Upon return the 71 &v4l2-subdev-format; contains the current format as would be returned by a 72 <constant>VIDIOC_SUBDEV_G_FMT</constant> call.</para> 73 74 <para>Applications can query the device capabilities by setting the 75 <structfield>which</structfield> to 76 <constant>V4L2_SUBDEV_FORMAT_TRY</constant>. When set, 'try' formats are not 77 applied to the device by the driver, but are changed exactly as active 78 formats and stored in the sub-device file handle. Two applications querying 79 the same sub-device would thus not interact with each other.</para> 80 81 <para>For instance, to try a format at the output pad of a sub-device, 82 applications would first set the try format at the sub-device input with the 83 <constant>VIDIOC_SUBDEV_S_FMT</constant> ioctl. They would then either 84 retrieve the default format at the output pad with the 85 <constant>VIDIOC_SUBDEV_G_FMT</constant> ioctl, or set the desired output 86 pad format with the <constant>VIDIOC_SUBDEV_S_FMT</constant> ioctl and check 87 the returned value.</para> 88 89 <para>Try formats do not depend on active formats, but can depend on the 90 current links configuration or sub-device controls value. For instance, a 91 low-pass noise filter might crop pixels at the frame boundaries, modifying 92 its output frame size.</para> 93 94 <para>Drivers must not return an error solely because the requested format 95 doesn't match the device capabilities. They must instead modify the format 96 to match what the hardware can provide. The modified format should be as 97 close as possible to the original request.</para> 98 99 <table pgwide="1" frame="none" id="v4l2-subdev-format"> 100 <title>struct <structname>v4l2_subdev_format</structname></title> 101 <tgroup cols="3"> 102 &cs-str; 103 <tbody valign="top"> 104 <row> 105 <entry>__u32</entry> 106 <entry><structfield>pad</structfield></entry> 107 <entry>Pad number as reported by the media controller API.</entry> 108 </row> 109 <row> 110 <entry>__u32</entry> 111 <entry><structfield>which</structfield></entry> 112 <entry>Format to modified, from &v4l2-subdev-format-whence;.</entry> 113 </row> 114 <row> 115 <entry>&v4l2-mbus-framefmt;</entry> 116 <entry><structfield>format</structfield></entry> 117 <entry>Definition of an image format, see <xref 118 linkend="v4l2-mbus-framefmt" /> for details.</entry> 119 </row> 120 <row> 121 <entry>__u32</entry> 122 <entry><structfield>reserved</structfield>[8]</entry> 123 <entry>Reserved for future extensions. Applications and drivers must 124 set the array to zero.</entry> 125 </row> 126 </tbody> 127 </tgroup> 128 </table> 129 130 <table pgwide="1" frame="none" id="v4l2-subdev-format-whence"> 131 <title>enum <structname>v4l2_subdev_format_whence</structname></title> 132 <tgroup cols="3"> 133 &cs-def; 134 <tbody valign="top"> 135 <row> 136 <entry>V4L2_SUBDEV_FORMAT_TRY</entry> 137 <entry>0</entry> 138 <entry>Try formats, used for querying device capabilities.</entry> 139 </row> 140 <row> 141 <entry>V4L2_SUBDEV_FORMAT_ACTIVE</entry> 142 <entry>1</entry> 143 <entry>Active formats, applied to the hardware.</entry> 144 </row> 145 </tbody> 146 </tgroup> 147 </table> 148 </refsect1> 149 150 <refsect1> 151 &return-value; 152 153 <variablelist> 154 <varlistentry> 155 <term><errorcode>EBUSY</errorcode></term> 156 <listitem> 157 <para>The format can't be changed because the pad is currently busy. 158 This can be caused, for instance, by an active video stream on the 159 pad. The ioctl must not be retried without performing another action 160 to fix the problem first. Only returned by 161 <constant>VIDIOC_SUBDEV_S_FMT</constant></para> 162 </listitem> 163 </varlistentry> 164 <varlistentry> 165 <term><errorcode>EINVAL</errorcode></term> 166 <listitem> 167 <para>The &v4l2-subdev-format; <structfield>pad</structfield> 168 references a non-existing pad, or the <structfield>which</structfield> 169 field references a non-existing format.</para> 170 </listitem> 171 </varlistentry> 172 </variablelist> 173 </refsect1> 174 <refsect1> 175 &return-value; 176 </refsect1> 177 </refentry>
