1 .. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
2 .. c:namespace:: V4L
3
4 .. _VIDIOC_SUBDEV_G_FMT:
5
6 **********************************************
7 ioctl VIDIOC_SUBDEV_G_FMT, VIDIOC_SUBDEV_S_FMT
8 **********************************************
9
10 Name
11 ====
12
13 VIDIOC_SUBDEV_G_FMT - VIDIOC_SUBDEV_S_FMT - Get or set the data format on a subdev pad
14
15 Synopsis
16 ========
17
18 .. c:macro:: VIDIOC_SUBDEV_G_FMT
19
20 ``int ioctl(int fd, VIDIOC_SUBDEV_G_FMT, struct v4l2_subdev_format *argp)``
21
22 .. c:macro:: VIDIOC_SUBDEV_S_FMT
23
24 ``int ioctl(int fd, VIDIOC_SUBDEV_S_FMT, struct v4l2_subdev_format *argp)``
25
26 Arguments
27 =========
28
29 ``fd``
30 File descriptor returned by :c:func:`open()`.
31
32 ``argp``
33 Pointer to struct :c:type:`v4l2_subdev_format`.
34
35 Description
36 ===========
37
38 These ioctls are used to negotiate the frame format at specific subdev
39 pads in the image pipeline.
40
41 To retrieve the current format applications set the ``pad`` field of a
42 struct :c:type:`v4l2_subdev_format` to the desired
43 pad number as reported by the media API and the ``which`` field to
44 ``V4L2_SUBDEV_FORMAT_ACTIVE``. When they call the
45 ``VIDIOC_SUBDEV_G_FMT`` ioctl with a pointer to this structure the
46 driver fills the members of the ``format`` field.
47
48 To change the current format applications set both the ``pad`` and
49 ``which`` fields and all members of the ``format`` field. When they call
50 the ``VIDIOC_SUBDEV_S_FMT`` ioctl with a pointer to this structure the
51 driver verifies the requested format, adjusts it based on the hardware
52 capabilities and configures the device. Upon return the struct
53 :c:type:`v4l2_subdev_format` contains the current
54 format as would be returned by a ``VIDIOC_SUBDEV_G_FMT`` call.
55
56 Applications can query the device capabilities by setting the ``which``
57 to ``V4L2_SUBDEV_FORMAT_TRY``. When set, 'try' formats are not applied
58 to the device by the driver, but are changed exactly as active formats
59 and stored in the sub-device file handle. Two applications querying the
60 same sub-device would thus not interact with each other.
61
62 For instance, to try a format at the output pad of a sub-device,
63 applications would first set the try format at the sub-device input with
64 the ``VIDIOC_SUBDEV_S_FMT`` ioctl. They would then either retrieve the
65 default format at the output pad with the ``VIDIOC_SUBDEV_G_FMT`` ioctl,
66 or set the desired output pad format with the ``VIDIOC_SUBDEV_S_FMT``
67 ioctl and check the returned value.
68
69 Try formats do not depend on active formats, but can depend on the
70 current links configuration or sub-device controls value. For instance,
71 a low-pass noise filter might crop pixels at the frame boundaries,
72 modifying its output frame size.
73
74 If the subdev device node has been registered in read-only mode, calls to
75 ``VIDIOC_SUBDEV_S_FMT`` are only valid if the ``which`` field is set to
76 ``V4L2_SUBDEV_FORMAT_TRY``, otherwise an error is returned and the errno
77 variable is set to ``-EPERM``.
78
79 Drivers must not return an error solely because the requested format
80 doesn't match the device capabilities. They must instead modify the
81 format to match what the hardware can provide. The modified format
82 should be as close as possible to the original request.
83
84 .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.5cm}|
85
86 .. c:type:: v4l2_subdev_format
87
88 .. flat-table:: struct v4l2_subdev_format
89 :header-rows: 0
90 :stub-columns: 0
91 :widths: 1 1 2
92
93 * - __u32
94 - ``pad``
95 - Pad number as reported by the media controller API.
96 * - __u32
97 - ``which``
98 - Format to modified, from enum
99 :ref:`v4l2_subdev_format_whence <v4l2-subdev-format-whence>`.
100 * - struct :c:type:`v4l2_mbus_framefmt`
101 - ``format``
102 - Definition of an image format, see :c:type:`v4l2_mbus_framefmt` for
103 details.
104 * - __u32
105 - ``stream``
106 - Stream identifier.
107 * - __u32
108 - ``reserved``\ [7]
109 - Reserved for future extensions. Applications and drivers must set
110 the array to zero.
111
112
113 .. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.5cm}|
114
115 .. _v4l2-subdev-format-whence:
116
117 .. flat-table:: enum v4l2_subdev_format_whence
118 :header-rows: 0
119 :stub-columns: 0
120 :widths: 3 1 4
121
122 * - V4L2_SUBDEV_FORMAT_TRY
123 - 0
124 - Try formats, used for querying device capabilities.
125 * - V4L2_SUBDEV_FORMAT_ACTIVE
126 - 1
127 - Active formats, applied to the hardware.
128
129 Return Value
130 ============
131
132 On success 0 is returned, on error -1 and the ``errno`` variable is set
133 appropriately. The generic error codes are described at the
134 :ref:`Generic Error Codes <gen-errors>` chapter.
135
136 EBUSY
137 The format can't be changed because the pad is currently busy. This
138 can be caused, for instance, by an active video stream on the pad.
139 The ioctl must not be retried without performing another action to
140 fix the problem first. Only returned by ``VIDIOC_SUBDEV_S_FMT``
141
142 EINVAL
143 The struct :c:type:`v4l2_subdev_format` ``pad`` references a non-existing
144 pad, or the ``which`` field has an unsupported value.
145
146 EPERM
147 The ``VIDIOC_SUBDEV_S_FMT`` ioctl has been called on a read-only subdevice
148 and the ``which`` field is set to ``V4L2_SUBDEV_FORMAT_ACTIVE``.
149
150 ============
151
152 On success 0 is returned, on error -1 and the ``errno`` variable is set
153 appropriately. The generic error codes are described at the
154 :ref:`Generic Error Codes <gen-errors>` chapter.
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