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  <refsect1>
181    &return-value;
182  </refsect1>
183</refentry>
184