vidioc-subdev-g-fmt.rst

  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.