1.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later 2.. c:namespace:: V4L 3 4.. _VIDIOC_SUBDEV_G_FMT: 5 6********************************************** 7ioctl VIDIOC_SUBDEV_G_FMT, VIDIOC_SUBDEV_S_FMT 8********************************************** 9 10Name 11==== 12 13VIDIOC_SUBDEV_G_FMT - VIDIOC_SUBDEV_S_FMT - Get or set the data format on a subdev pad 14 15Synopsis 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 26Arguments 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 35Description 36=========== 37 38These ioctls are used to negotiate the frame format at specific subdev 39pads in the image pipeline. 40 41To retrieve the current format applications set the ``pad`` field of a 42struct :c:type:`v4l2_subdev_format` to the desired 43pad 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 46driver fills the members of the ``format`` field. 47 48To change the current format applications set both the ``pad`` and 49``which`` fields and all members of the ``format`` field. When they call 50the ``VIDIOC_SUBDEV_S_FMT`` ioctl with a pointer to this structure the 51driver verifies the requested format, adjusts it based on the hardware 52capabilities and configures the device. Upon return the struct 53:c:type:`v4l2_subdev_format` contains the current 54format as would be returned by a ``VIDIOC_SUBDEV_G_FMT`` call. 55 56Applications can query the device capabilities by setting the ``which`` 57to ``V4L2_SUBDEV_FORMAT_TRY``. When set, 'try' formats are not applied 58to the device by the driver, but are changed exactly as active formats 59and stored in the sub-device file handle. Two applications querying the 60same sub-device would thus not interact with each other. 61 62For instance, to try a format at the output pad of a sub-device, 63applications would first set the try format at the sub-device input with 64the ``VIDIOC_SUBDEV_S_FMT`` ioctl. They would then either retrieve the 65default format at the output pad with the ``VIDIOC_SUBDEV_G_FMT`` ioctl, 66or set the desired output pad format with the ``VIDIOC_SUBDEV_S_FMT`` 67ioctl and check the returned value. 68 69Try formats do not depend on active formats, but can depend on the 70current links configuration or sub-device controls value. For instance, 71a low-pass noise filter might crop pixels at the frame boundaries, 72modifying its output frame size. 73 74If 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 77variable is set to ``-EPERM``. 78 79Drivers must not return an error solely because the requested format 80doesn't match the device capabilities. They must instead modify the 81format to match what the hardware can provide. The modified format 82should 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 129Return Value 130============ 131 132On success 0 is returned, on error -1 and the ``errno`` variable is set 133appropriately. The generic error codes are described at the 134:ref:`Generic Error Codes <gen-errors>` chapter. 135 136EBUSY 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 142EINVAL 143 The struct :c:type:`v4l2_subdev_format` ``pad`` references a non-existing 144 pad, or the ``which`` field has an unsupported value. 145 146EPERM 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 152On success 0 is returned, on error -1 and the ``errno`` variable is set 153appropriately. The generic error codes are described at the 154:ref:`Generic Error Codes <gen-errors>` chapter. 155