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/userspace-api/media/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 81If the subdev device node has been registered in read-only mode, calls to 82``VIDIOC_SUBDEV_S_FMT`` are only valid if the ``which`` field is set to 83``V4L2_SUBDEV_FORMAT_TRY``, otherwise an error is returned and the errno 84variable is set to ``-EPERM``. 85 86Drivers must not return an error solely because the requested format 87doesn't match the device capabilities. They must instead modify the 88format to match what the hardware can provide. The modified format 89should be as close as possible to the original request. 90 91 92.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}| 93 94.. c:type:: v4l2_subdev_format 95 96.. flat-table:: struct v4l2_subdev_format 97 :header-rows: 0 98 :stub-columns: 0 99 :widths: 1 1 2 100 101 * - __u32 102 - ``pad`` 103 - Pad number as reported by the media controller API. 104 * - __u32 105 - ``which`` 106 - Format to modified, from enum 107 :ref:`v4l2_subdev_format_whence <v4l2-subdev-format-whence>`. 108 * - struct :c:type:`v4l2_mbus_framefmt` 109 - ``format`` 110 - Definition of an image format, see :c:type:`v4l2_mbus_framefmt` for 111 details. 112 * - __u32 113 - ``reserved``\ [8] 114 - Reserved for future extensions. Applications and drivers must set 115 the array to zero. 116 117 118 119.. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.7cm}| 120 121.. _v4l2-subdev-format-whence: 122 123.. flat-table:: enum v4l2_subdev_format_whence 124 :header-rows: 0 125 :stub-columns: 0 126 :widths: 3 1 4 127 128 * - V4L2_SUBDEV_FORMAT_TRY 129 - 0 130 - Try formats, used for querying device capabilities. 131 * - V4L2_SUBDEV_FORMAT_ACTIVE 132 - 1 133 - Active formats, applied to the hardware. 134 135 136Return Value 137============ 138 139On success 0 is returned, on error -1 and the ``errno`` variable is set 140appropriately. The generic error codes are described at the 141:ref:`Generic Error Codes <gen-errors>` chapter. 142 143EBUSY 144 The format can't be changed because the pad is currently busy. This 145 can be caused, for instance, by an active video stream on the pad. 146 The ioctl must not be retried without performing another action to 147 fix the problem first. Only returned by ``VIDIOC_SUBDEV_S_FMT`` 148 149EINVAL 150 The struct :c:type:`v4l2_subdev_format` 151 ``pad`` references a non-existing pad, or the ``which`` field 152 references a non-existing format. 153 154EPERM 155 The ``VIDIOC_SUBDEV_S_FMT`` ioctl has been called on a read-only subdevice 156 and the ``which`` field is set to ``V4L2_SUBDEV_FORMAT_ACTIVE``. 157 158============ 159 160On success 0 is returned, on error -1 and the ``errno`` variable is set 161appropriately. The generic error codes are described at the 162:ref:`Generic Error Codes <gen-errors>` chapter. 163