vidioc-g-edid.rst

  1.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
  2.. c:namespace:: V4L
  3
  4.. _VIDIOC_G_EDID:
  5
  6******************************************************************************
  7ioctl VIDIOC_G_EDID, VIDIOC_S_EDID, VIDIOC_SUBDEV_G_EDID, VIDIOC_SUBDEV_S_EDID
  8******************************************************************************
  9
 10Name
 11====
 12
 13VIDIOC_G_EDID - VIDIOC_S_EDID - VIDIOC_SUBDEV_G_EDID - VIDIOC_SUBDEV_S_EDID - Get or set the EDID of a video receiver/transmitter
 14
 15Synopsis
 16========
 17
 18.. c:macro:: VIDIOC_G_EDID
 19
 20``int ioctl(int fd, VIDIOC_G_EDID, struct v4l2_edid *argp)``
 21
 22.. c:macro:: VIDIOC_S_EDID
 23
 24``int ioctl(int fd, VIDIOC_S_EDID, struct v4l2_edid *argp)``
 25
 26.. c:macro:: VIDIOC_SUBDEV_G_EDID
 27
 28``int ioctl(int fd, VIDIOC_SUBDEV_G_EDID, struct v4l2_edid *argp)``
 29
 30.. c:macro:: VIDIOC_SUBDEV_S_EDID
 31
 32``int ioctl(int fd, VIDIOC_SUBDEV_S_EDID, struct v4l2_edid *argp)``
 33
 34Arguments
 35=========
 36
 37``fd``
 38    File descriptor returned by :c:func:`open()`.
 39
 40``argp``
 41   Pointer to struct :c:type:`v4l2_edid`.
 42
 43Description
 44===========
 45
 46These ioctls can be used to get or set an EDID associated with an input
 47from a receiver or an output of a transmitter device. They can be used
 48with subdevice nodes (/dev/v4l-subdevX) or with video nodes
 49(/dev/videoX).
 50
 51When used with video nodes the ``pad`` field represents the input (for
 52video capture devices) or output (for video output devices) index as is
 53returned by :ref:`VIDIOC_ENUMINPUT` and
 54:ref:`VIDIOC_ENUMOUTPUT` respectively. When used
 55with subdevice nodes the ``pad`` field represents the input or output
 56pad of the subdevice. If there is no EDID support for the given ``pad``
 57value, then the ``EINVAL`` error code will be returned.
 58
 59To get the EDID data the application has to fill in the ``pad``,
 60``start_block``, ``blocks`` and ``edid`` fields, zero the ``reserved``
 61array and call :ref:`VIDIOC_G_EDID <VIDIOC_G_EDID>`. The current EDID from block
 62``start_block`` and of size ``blocks`` will be placed in the memory
 63``edid`` points to. The ``edid`` pointer must point to memory at least
 64``blocks`` * 128 bytes large (the size of one block is 128 bytes).
 65
 66If there are fewer blocks than specified, then the driver will set
 67``blocks`` to the actual number of blocks. If there are no EDID blocks
 68available at all, then the error code ``ENODATA`` is set.
 69
 70If blocks have to be retrieved from the sink, then this call will block
 71until they have been read.
 72
 73If ``start_block`` and ``blocks`` are both set to 0 when
 74:ref:`VIDIOC_G_EDID <VIDIOC_G_EDID>` is called, then the driver will set ``blocks`` to the
 75total number of available EDID blocks and it will return 0 without
 76copying any data. This is an easy way to discover how many EDID blocks
 77there are.
 78
 79.. note::
 80
 81   If there are no EDID blocks available at all, then
 82   the driver will set ``blocks`` to 0 and it returns 0.
 83
 84To set the EDID blocks of a receiver the application has to fill in the
 85``pad``, ``blocks`` and ``edid`` fields, set ``start_block`` to 0 and
 86zero the ``reserved`` array. It is not possible to set part of an EDID,
 87it is always all or nothing. Setting the EDID data is only valid for
 88receivers as it makes no sense for a transmitter.
 89
 90The driver assumes that the full EDID is passed in. If there are more
 91EDID blocks than the hardware can handle then the EDID is not written,
 92but instead the error code ``E2BIG`` is set and ``blocks`` is set to the
 93maximum that the hardware supports. If ``start_block`` is any value
 94other than 0 then the error code ``EINVAL`` is set.
 95
 96To disable an EDID you set ``blocks`` to 0. Depending on the hardware
 97this will drive the hotplug pin low and/or block the source from reading
 98the EDID data in some way. In any case, the end result is the same: the
 99EDID is no longer available.
100
101.. c:type:: v4l2_edid
102
103.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.5cm}|
104
105.. flat-table:: struct v4l2_edid
106    :header-rows:  0
107    :stub-columns: 0
108    :widths:       1 1 2
109
110    * - __u32
111      - ``pad``
112      - Pad for which to get/set the EDID blocks. When used with a video
113	device node the pad represents the input or output index as
114	returned by :ref:`VIDIOC_ENUMINPUT` and
115	:ref:`VIDIOC_ENUMOUTPUT` respectively.
116    * - __u32
117      - ``start_block``
118      - Read the EDID from starting with this block. Must be 0 when
119	setting the EDID.
120    * - __u32
121      - ``blocks``
122      - The number of blocks to get or set. Must be less or equal to 256
123	(the maximum number of blocks as defined by the standard). When
124	you set the EDID and ``blocks`` is 0, then the EDID is disabled or
125	erased.
126    * - __u32
127      - ``reserved``\ [5]
128      - Reserved for future extensions. Applications and drivers must set
129	the array to zero.
130    * - __u8 *
131      - ``edid``
132      - Pointer to memory that contains the EDID. The minimum size is
133	``blocks`` * 128.
134
135Return Value
136============
137
138On success 0 is returned, on error -1 and the ``errno`` variable is set
139appropriately. The generic error codes are described at the
140:ref:`Generic Error Codes <gen-errors>` chapter.
141
142``ENODATA``
143    The EDID data is not available.
144
145``E2BIG``
146    The EDID data you provided is more than the hardware can handle.