tjh.dev
Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
os
linux
1.. -*- coding: utf-8; mode: rst -*-
2
3.. _VIDIOC_G_EDID:
4
5******************************************************************************
6ioctl VIDIOC_G_EDID, VIDIOC_S_EDID, VIDIOC_SUBDEV_G_EDID, VIDIOC_SUBDEV_S_EDID
7******************************************************************************
8
9Name
10====
11
12VIDIOC_G_EDID - VIDIOC_S_EDID - VIDIOC_SUBDEV_G_EDID - VIDIOC_SUBDEV_S_EDID - Get or set the EDID of a video receiver/transmitter
13
14
15Synopsis
16========
17
18.. c:function:: int ioctl( int fd, VIDIOC_G_EDID, struct v4l2_edid *argp )
19 :name: VIDIOC_G_EDID
20
21.. c:function:: int ioctl( int fd, VIDIOC_S_EDID, struct v4l2_edid *argp )
22 :name: VIDIOC_S_EDID
23
24
25.. c:function:: int ioctl( int fd, VIDIOC_SUBDEV_G_EDID, struct v4l2_edid *argp )
26 :name: VIDIOC_SUBDEV_G_EDID
27
28.. c:function:: int ioctl( int fd, VIDIOC_SUBDEV_S_EDID, struct v4l2_edid *argp )
29 :name: VIDIOC_SUBDEV_S_EDID
30
31
32Arguments
33=========
34
35``fd``
36 File descriptor returned by :ref:`open() <func-open>`.
37
38``argp``
39
40
41Description
42===========
43
44These ioctls can be used to get or set an EDID associated with an input
45from a receiver or an output of a transmitter device. They can be used
46with subdevice nodes (/dev/v4l-subdevX) or with video nodes
47(/dev/videoX).
48
49When used with video nodes the ``pad`` field represents the input (for
50video capture devices) or output (for video output devices) index as is
51returned by :ref:`VIDIOC_ENUMINPUT` and
52:ref:`VIDIOC_ENUMOUTPUT` respectively. When used
53with subdevice nodes the ``pad`` field represents the input or output
54pad of the subdevice. If there is no EDID support for the given ``pad``
55value, then the ``EINVAL`` error code will be returned.
56
57To get the EDID data the application has to fill in the ``pad``,
58``start_block``, ``blocks`` and ``edid`` fields, zero the ``reserved``
59array and call :ref:`VIDIOC_G_EDID <VIDIOC_G_EDID>`. The current EDID from block
60``start_block`` and of size ``blocks`` will be placed in the memory
61``edid`` points to. The ``edid`` pointer must point to memory at least
62``blocks`` * 128 bytes large (the size of one block is 128 bytes).
63
64If there are fewer blocks than specified, then the driver will set
65``blocks`` to the actual number of blocks. If there are no EDID blocks
66available at all, then the error code ``ENODATA`` is set.
67
68If blocks have to be retrieved from the sink, then this call will block
69until they have been read.
70
71If ``start_block`` and ``blocks`` are both set to 0 when
72:ref:`VIDIOC_G_EDID <VIDIOC_G_EDID>` is called, then the driver will set ``blocks`` to the
73total number of available EDID blocks and it will return 0 without
74copying any data. This is an easy way to discover how many EDID blocks
75there are.
76
77.. note::
78
79 If there are no EDID blocks available at all, then
80 the driver will set ``blocks`` to 0 and it returns 0.
81
82To set the EDID blocks of a receiver the application has to fill in the
83``pad``, ``blocks`` and ``edid`` fields, set ``start_block`` to 0 and
84zero the ``reserved`` array. It is not possible to set part of an EDID,
85it is always all or nothing. Setting the EDID data is only valid for
86receivers as it makes no sense for a transmitter.
87
88The driver assumes that the full EDID is passed in. If there are more
89EDID blocks than the hardware can handle then the EDID is not written,
90but instead the error code ``E2BIG`` is set and ``blocks`` is set to the
91maximum that the hardware supports. If ``start_block`` is any value
92other than 0 then the error code ``EINVAL`` is set.
93
94To disable an EDID you set ``blocks`` to 0. Depending on the hardware
95this will drive the hotplug pin low and/or block the source from reading
96the EDID data in some way. In any case, the end result is the same: the
97EDID is no longer available.
98
99
100.. c:type:: v4l2_edid
101
102.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
103
104.. flat-table:: struct v4l2_edid
105 :header-rows: 0
106 :stub-columns: 0
107 :widths: 1 1 2
108
109 * - __u32
110 - ``pad``
111 - Pad for which to get/set the EDID blocks. When used with a video
112 device node the pad represents the input or output index as
113 returned by :ref:`VIDIOC_ENUMINPUT` and
114 :ref:`VIDIOC_ENUMOUTPUT` respectively.
115 * - __u32
116 - ``start_block``
117 - Read the EDID from starting with this block. Must be 0 when
118 setting the EDID.
119 * - __u32
120 - ``blocks``
121 - The number of blocks to get or set. Must be less or equal to 256
122 (the maximum number of blocks as defined by the standard). When
123 you set the EDID and ``blocks`` is 0, then the EDID is disabled or
124 erased.
125 * - __u32
126 - ``reserved``\ [5]
127 - Reserved for future extensions. Applications and drivers must set
128 the array to zero.
129 * - __u8 *
130 - ``edid``
131 - Pointer to memory that contains the EDID. The minimum size is
132 ``blocks`` * 128.
133
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.