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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>
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