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1 | .. -*- coding: utf-8; mode: rst -*- |
2 | ||
af4a4d0d | 3 | .. _VIDIOC_SUBDEV_G_FMT: |
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4 | |
5 | ********************************************** | |
6 | ioctl VIDIOC_SUBDEV_G_FMT, VIDIOC_SUBDEV_S_FMT | |
7 | ********************************************** | |
8 | ||
15e7d615 | 9 | Name |
586027ce | 10 | ==== |
5377d91f | 11 | |
586027ce | 12 | VIDIOC_SUBDEV_G_FMT - VIDIOC_SUBDEV_S_FMT - Get or set the data format on a subdev pad |
5377d91f | 13 | |
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14 | |
15 | Synopsis | |
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16 | ======== |
17 | ||
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18 | .. c:function:: int ioctl( int fd, VIDIOC_SUBDEV_G_FMT, struct v4l2_subdev_format *argp ) |
19 | :name: VIDIOC_SUBDEV_G_FMT | |
20 | ||
21 | .. c:function:: int ioctl( int fd, VIDIOC_SUBDEV_S_FMT, struct v4l2_subdev_format *argp ) | |
22 | :name: VIDIOC_SUBDEV_S_FMT | |
5377d91f | 23 | |
586027ce | 24 | |
15e7d615 | 25 | Arguments |
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26 | ========= |
27 | ||
28 | ``fd`` | |
29 | File descriptor returned by :ref:`open() <func-open>`. | |
30 | ||
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31 | ``argp`` |
32 | ||
33 | ||
15e7d615 | 34 | Description |
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35 | =========== |
36 | ||
37 | These ioctls are used to negotiate the frame format at specific subdev | |
38 | pads in the image pipeline. | |
39 | ||
40 | To retrieve the current format applications set the ``pad`` field of a | |
ffa0441e | 41 | struct :c:type:`v4l2_subdev_format` to the desired |
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42 | pad number as reported by the media API and the ``which`` field to |
43 | ``V4L2_SUBDEV_FORMAT_ACTIVE``. When they call the | |
44 | ``VIDIOC_SUBDEV_G_FMT`` ioctl with a pointer to this structure the | |
45 | driver fills the members of the ``format`` field. | |
46 | ||
47 | To change the current format applications set both the ``pad`` and | |
48 | ``which`` fields and all members of the ``format`` field. When they call | |
49 | the ``VIDIOC_SUBDEV_S_FMT`` ioctl with a pointer to this structure the | |
50 | driver verifies the requested format, adjusts it based on the hardware | |
51 | capabilities and configures the device. Upon return the struct | |
ffa0441e | 52 | :c:type:`v4l2_subdev_format` contains the current |
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53 | format as would be returned by a ``VIDIOC_SUBDEV_G_FMT`` call. |
54 | ||
55 | Applications can query the device capabilities by setting the ``which`` | |
56 | to ``V4L2_SUBDEV_FORMAT_TRY``. When set, 'try' formats are not applied | |
57 | to the device by the driver, but are changed exactly as active formats | |
58 | and stored in the sub-device file handle. Two applications querying the | |
59 | same sub-device would thus not interact with each other. | |
60 | ||
61 | For instance, to try a format at the output pad of a sub-device, | |
62 | applications would first set the try format at the sub-device input with | |
63 | the ``VIDIOC_SUBDEV_S_FMT`` ioctl. They would then either retrieve the | |
64 | default format at the output pad with the ``VIDIOC_SUBDEV_G_FMT`` ioctl, | |
65 | or set the desired output pad format with the ``VIDIOC_SUBDEV_S_FMT`` | |
66 | ioctl and check the returned value. | |
67 | ||
68 | Try formats do not depend on active formats, but can depend on the | |
69 | current links configuration or sub-device controls value. For instance, | |
70 | a low-pass noise filter might crop pixels at the frame boundaries, | |
71 | modifying its output frame size. | |
72 | ||
73 | Drivers must not return an error solely because the requested format | |
74 | doesn't match the device capabilities. They must instead modify the | |
75 | format to match what the hardware can provide. The modified format | |
76 | should be as close as possible to the original request. | |
77 | ||
78 | ||
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79 | .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}| |
80 | ||
ffa0441e | 81 | .. c:type:: v4l2_subdev_format |
fa92b04d | 82 | |
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83 | .. flat-table:: struct v4l2_subdev_format |
84 | :header-rows: 0 | |
85 | :stub-columns: 0 | |
86 | :widths: 1 1 2 | |
87 | ||
88 | ||
89 | - .. row 1 | |
90 | ||
91 | - __u32 | |
92 | ||
93 | - ``pad`` | |
94 | ||
95 | - Pad number as reported by the media controller API. | |
96 | ||
97 | - .. row 2 | |
98 | ||
99 | - __u32 | |
100 | ||
101 | - ``which`` | |
102 | ||
103 | - Format to modified, from enum | |
0579e6e3 | 104 | :ref:`v4l2_subdev_format_whence <v4l2-subdev-format-whence>`. |
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105 | |
106 | - .. row 3 | |
107 | ||
ffa0441e | 108 | - struct :c:type:`v4l2_mbus_framefmt` |
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109 | |
110 | - ``format`` | |
111 | ||
56683d7d | 112 | - Definition of an image format, see :c:type:`v4l2_mbus_framefmt` for |
0579e6e3 | 113 | details. |
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114 | |
115 | - .. row 4 | |
116 | ||
117 | - __u32 | |
118 | ||
8968da9b | 119 | - ``reserved``\ [8] |
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120 | |
121 | - Reserved for future extensions. Applications and drivers must set | |
0579e6e3 | 122 | the array to zero. |
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123 | |
124 | ||
125 | ||
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126 | .. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.7cm}| |
127 | ||
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128 | .. _v4l2-subdev-format-whence: |
129 | ||
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130 | .. flat-table:: enum v4l2_subdev_format_whence |
131 | :header-rows: 0 | |
132 | :stub-columns: 0 | |
133 | :widths: 3 1 4 | |
134 | ||
135 | ||
136 | - .. row 1 | |
137 | ||
138 | - V4L2_SUBDEV_FORMAT_TRY | |
139 | ||
140 | - 0 | |
141 | ||
142 | - Try formats, used for querying device capabilities. | |
143 | ||
144 | - .. row 2 | |
145 | ||
146 | - V4L2_SUBDEV_FORMAT_ACTIVE | |
147 | ||
148 | - 1 | |
149 | ||
150 | - Active formats, applied to the hardware. | |
151 | ||
152 | ||
15e7d615 | 153 | Return Value |
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154 | ============ |
155 | ||
156 | On success 0 is returned, on error -1 and the ``errno`` variable is set | |
157 | appropriately. The generic error codes are described at the | |
158 | :ref:`Generic Error Codes <gen-errors>` chapter. | |
159 | ||
160 | EBUSY | |
161 | The format can't be changed because the pad is currently busy. This | |
162 | can be caused, for instance, by an active video stream on the pad. | |
163 | The ioctl must not be retried without performing another action to | |
164 | fix the problem first. Only returned by ``VIDIOC_SUBDEV_S_FMT`` | |
165 | ||
166 | EINVAL | |
ffa0441e | 167 | The struct :c:type:`v4l2_subdev_format` |
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168 | ``pad`` references a non-existing pad, or the ``which`` field |
169 | references a non-existing format. | |
170 | ||
171 | ||
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172 | ============ |
173 | ||
174 | On success 0 is returned, on error -1 and the ``errno`` variable is set | |
175 | appropriately. The generic error codes are described at the | |
176 | :ref:`Generic Error Codes <gen-errors>` chapter. |