projects / linux-2.6-block.git / blame
| Commit | Line | Data |
|---|---|---|
| 059b1c5b | 1 | .. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later |
| 82559ac0 | 2 | |
| af4a4d0d | 3 | .. _VIDIOC_QUERYSTD: |
| 5377d91f | 4 | |
| 56ab8cdb NS |
5 | ********************************************* |
| 6 | ioctl VIDIOC_QUERYSTD, VIDIOC_SUBDEV_QUERYSTD | |
| 7 | ********************************************* | |
| 5377d91f | 8 | |
| 15e7d615 | 9 | Name |
| 586027ce | 10 | ==== |
| 5377d91f | 11 | |
| 56ab8cdb | 12 | VIDIOC_QUERYSTD - VIDIOC_SUBDEV_QUERYSTD - Sense the video standard received by the current input |
| 5377d91f | 13 | |
| 15e7d615 MCC |
14 | |
| 15 | Synopsis | |
| 5377d91f MH |
16 | ======== |
| 17 | ||
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18 | .. c:function:: int ioctl( int fd, VIDIOC_QUERYSTD, v4l2_std_id *argp ) |
| 19 | :name: VIDIOC_QUERYSTD | |
| 5377d91f | 20 | |
| 56ab8cdb NS |
21 | .. c:function:: int ioctl( int fd, VIDIOC_SUBDEV_QUERYSTD, v4l2_std_id *argp ) |
| 22 | :name: VIDIOC_SUBDEV_QUERYSTD | |
| 23 | ||
| 586027ce | 24 | |
| 15e7d615 | 25 | Arguments |
| 5377d91f MH |
26 | ========= |
| 27 | ||
| 28 | ``fd`` | |
| 29 | File descriptor returned by :ref:`open() <func-open>`. | |
| 30 | ||
| 5377d91f | 31 | ``argp`` |
| 1473c75e | 32 | Pointer to :c:type:`v4l2_std_id`. |
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33 | |
| 34 | ||
| 15e7d615 | 35 | Description |
| 5377d91f MH |
36 | =========== |
| 37 | ||
| 38 | The hardware may be able to detect the current video standard | |
| 2212ff25 | 39 | automatically. To do so, applications call :ref:`VIDIOC_QUERYSTD` with a |
| 5377d91f MH |
40 | pointer to a :ref:`v4l2_std_id <v4l2-std-id>` type. The driver |
| 41 | stores here a set of candidates, this can be a single flag or a set of | |
| 42 | supported standards if for example the hardware can only distinguish | |
| 43 | between 50 and 60 Hz systems. If no signal was detected, then the driver | |
| 44 | will return V4L2_STD_UNKNOWN. When detection is not possible or fails, | |
| 45 | the set must contain all standards supported by the current video input | |
| 46 | or output. | |
| 47 | ||
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48 | .. note:: |
| 49 | ||
| 50 | Drivers shall *not* switch the video standard | |
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51 | automatically if a new video standard is detected. Instead, drivers |
| 52 | should send the ``V4L2_EVENT_SOURCE_CHANGE`` event (if they support | |
| 53 | this) and expect that userspace will take action by calling | |
| 54 | :ref:`VIDIOC_QUERYSTD`. The reason is that a new video standard can mean | |
| 55 | different buffer sizes as well, and you cannot change buffer sizes on | |
| 56 | the fly. In general, applications that receive the Source Change event | |
| 57 | will have to call :ref:`VIDIOC_QUERYSTD`, and if the detected video | |
| 58 | standard is valid they will have to stop streaming, set the new | |
| 59 | standard, allocate new buffers and start streaming again. | |
| 5377d91f MH |
60 | |
| 61 | ||
| 15e7d615 | 62 | Return Value |
| 5377d91f MH |
63 | ============ |
| 64 | ||
| 65 | On success 0 is returned, on error -1 and the ``errno`` variable is set | |
| 66 | appropriately. The generic error codes are described at the | |
| 67 | :ref:`Generic Error Codes <gen-errors>` chapter. | |
| 68 | ||
| 69 | ENODATA | |
| 70 | Standard video timings are not supported for this input or output. |