1.. Permission is granted to copy, distribute and/or modify this 2.. document under the terms of the GNU Free Documentation License, 3.. Version 1.1 or any later version published by the Free Software 4.. Foundation, with no Invariant Sections, no Front-Cover Texts 5.. and no Back-Cover Texts. A copy of the license is included at 6.. Documentation/media/uapi/fdl-appendix.rst. 7.. 8.. TODO: replace it to GFDL-1.1-or-later WITH no-invariant-sections 9 10.. _VIDIOC_SUBDEV_G_FMT: 11 12********************************************** 13ioctl VIDIOC_SUBDEV_G_FMT, VIDIOC_SUBDEV_S_FMT 14********************************************** 15 16Name 17==== 18 19VIDIOC_SUBDEV_G_FMT - VIDIOC_SUBDEV_S_FMT - Get or set the data format on a subdev pad 20 21 22Synopsis 23======== 24 25.. c:function:: int ioctl( int fd, VIDIOC_SUBDEV_G_FMT, struct v4l2_subdev_format *argp ) 26 :name: VIDIOC_SUBDEV_G_FMT 27 28.. c:function:: int ioctl( int fd, VIDIOC_SUBDEV_S_FMT, struct v4l2_subdev_format *argp ) 29 :name: VIDIOC_SUBDEV_S_FMT 30 31 32Arguments 33========= 34 35``fd`` 36 File descriptor returned by :ref:`open() <func-open>`. 37 38``argp`` 39 Pointer to struct :c:type:`v4l2_subdev_format`. 40 41 42Description 43=========== 44 45These ioctls are used to negotiate the frame format at specific subdev 46pads in the image pipeline. 47 48To retrieve the current format applications set the ``pad`` field of a 49struct :c:type:`v4l2_subdev_format` to the desired 50pad number as reported by the media API and the ``which`` field to 51``V4L2_SUBDEV_FORMAT_ACTIVE``. When they call the 52``VIDIOC_SUBDEV_G_FMT`` ioctl with a pointer to this structure the 53driver fills the members of the ``format`` field. 54 55To change the current format applications set both the ``pad`` and 56``which`` fields and all members of the ``format`` field. When they call 57the ``VIDIOC_SUBDEV_S_FMT`` ioctl with a pointer to this structure the 58driver verifies the requested format, adjusts it based on the hardware 59capabilities and configures the device. Upon return the struct 60:c:type:`v4l2_subdev_format` contains the current 61format as would be returned by a ``VIDIOC_SUBDEV_G_FMT`` call. 62 63Applications can query the device capabilities by setting the ``which`` 64to ``V4L2_SUBDEV_FORMAT_TRY``. When set, 'try' formats are not applied 65to the device by the driver, but are changed exactly as active formats 66and stored in the sub-device file handle. Two applications querying the 67same sub-device would thus not interact with each other. 68 69For instance, to try a format at the output pad of a sub-device, 70applications would first set the try format at the sub-device input with 71the ``VIDIOC_SUBDEV_S_FMT`` ioctl. They would then either retrieve the 72default format at the output pad with the ``VIDIOC_SUBDEV_G_FMT`` ioctl, 73or set the desired output pad format with the ``VIDIOC_SUBDEV_S_FMT`` 74ioctl and check the returned value. 75 76Try formats do not depend on active formats, but can depend on the 77current links configuration or sub-device controls value. For instance, 78a low-pass noise filter might crop pixels at the frame boundaries, 79modifying its output frame size. 80 81Drivers must not return an error solely because the requested format 82doesn't match the device capabilities. They must instead modify the 83format to match what the hardware can provide. The modified format 84should be as close as possible to the original request. 85 86 87.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}| 88 89.. c:type:: v4l2_subdev_format 90 91.. flat-table:: struct v4l2_subdev_format 92 :header-rows: 0 93 :stub-columns: 0 94 :widths: 1 1 2 95 96 * - __u32 97 - ``pad`` 98 - Pad number as reported by the media controller API. 99 * - __u32 100 - ``which`` 101 - Format to modified, from enum 102 :ref:`v4l2_subdev_format_whence <v4l2-subdev-format-whence>`. 103 * - struct :c:type:`v4l2_mbus_framefmt` 104 - ``format`` 105 - Definition of an image format, see :c:type:`v4l2_mbus_framefmt` for 106 details. 107 * - __u32 108 - ``reserved``\ [8] 109 - Reserved for future extensions. Applications and drivers must set 110 the array to zero. 111 112 113 114.. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.7cm}| 115 116.. _v4l2-subdev-format-whence: 117 118.. flat-table:: enum v4l2_subdev_format_whence 119 :header-rows: 0 120 :stub-columns: 0 121 :widths: 3 1 4 122 123 * - V4L2_SUBDEV_FORMAT_TRY 124 - 0 125 - Try formats, used for querying device capabilities. 126 * - V4L2_SUBDEV_FORMAT_ACTIVE 127 - 1 128 - Active formats, applied to the hardware. 129 130 131Return Value 132============ 133 134On success 0 is returned, on error -1 and the ``errno`` variable is set 135appropriately. The generic error codes are described at the 136:ref:`Generic Error Codes <gen-errors>` chapter. 137 138EBUSY 139 The format can't be changed because the pad is currently busy. This 140 can be caused, for instance, by an active video stream on the pad. 141 The ioctl must not be retried without performing another action to 142 fix the problem first. Only returned by ``VIDIOC_SUBDEV_S_FMT`` 143 144EINVAL 145 The struct :c:type:`v4l2_subdev_format` 146 ``pad`` references a non-existing pad, or the ``which`` field 147 references a non-existing format. 148 149 150============ 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