1 .. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
2 .. c:namespace:: V4L
3
4 .. _VIDIOC_DBG_G_REGISTER:
5
6 **************************************************
7 ioctl VIDIOC_DBG_G_REGISTER, VIDIOC_DBG_S_REGISTER
8 **************************************************
9
10 Name
11 ====
12
13 VIDIOC_DBG_G_REGISTER - VIDIOC_DBG_S_REGISTER - Read or write hardware registers
14
15 Synopsis
16 ========
17
18 .. c:macro:: VIDIOC_DBG_G_REGISTER
19
20 ``int ioctl(int fd, VIDIOC_DBG_G_REGISTER, struct v4l2_dbg_register *argp)``
21
22 .. c:macro:: VIDIOC_DBG_S_REGISTER
23
24 ``int ioctl(int fd, VIDIOC_DBG_S_REGISTER, const struct v4l2_dbg_register *argp)``
25
26 Arguments
27 =========
28
29 ``fd``
30 File descriptor returned by :c:func:`open()`.
31
32 ``argp``
33 Pointer to struct :c:type:`v4l2_dbg_register`.
34
35 Description
36 ===========
37
38 .. note::
39
40 This is an :ref:`experimental` interface and may
41 change in the future.
42
43 For driver debugging purposes these ioctls allow test applications to
44 access hardware registers directly. Regular applications must not use
45 them.
46
47 Since writing or even reading registers can jeopardize the system
48 security, its stability and damage the hardware, both ioctls require
49 superuser privileges. Additionally the Linux kernel must be compiled
50 with the ``CONFIG_VIDEO_ADV_DEBUG`` option to enable these ioctls.
51
52 To write a register applications must initialize all fields of a struct
53 :c:type:`v4l2_dbg_register` except for ``size`` and
54 call ``VIDIOC_DBG_S_REGISTER`` with a pointer to this structure. The
55 ``match.type`` and ``match.addr`` or ``match.name`` fields select a chip
56 on the TV card, the ``reg`` field specifies a register number and the
57 ``val`` field the value to be written into the register.
58
59 To read a register applications must initialize the ``match.type``,
60 ``match.addr`` or ``match.name`` and ``reg`` fields, and call
61 ``VIDIOC_DBG_G_REGISTER`` with a pointer to this structure. On success
62 the driver stores the register value in the ``val`` field and the size
63 (in bytes) of the value in ``size``.
64
65 When ``match.type`` is ``V4L2_CHIP_MATCH_BRIDGE``, ``match.addr``
66 selects the nth non-sub-device chip on the TV card. The number zero
67 always selects the host chip, e. g. the chip connected to the PCI or USB
68 bus. You can find out which chips are present with the
69 :ref:`VIDIOC_DBG_G_CHIP_INFO` ioctl.
70
71 When ``match.type`` is ``V4L2_CHIP_MATCH_SUBDEV``, ``match.addr``
72 selects the nth sub-device.
73
74 These ioctls are optional, not all drivers may support them. However
75 when a driver supports these ioctls it must also support
76 :ref:`VIDIOC_DBG_G_CHIP_INFO`. Conversely
77 it may support ``VIDIOC_DBG_G_CHIP_INFO`` but not these ioctls.
78
79 ``VIDIOC_DBG_G_REGISTER`` and ``VIDIOC_DBG_S_REGISTER`` were introduced
80 in Linux 2.6.21, but their API was changed to the one described here in
81 kernel 2.6.29.
82
83 We recommended the v4l2-dbg utility over calling these ioctls directly.
84 It is available from the LinuxTV v4l-dvb repository; see
85 `https://linuxtv.org/repo/ <https://linuxtv.org/repo/>`__ for access
86 instructions.
87
88 .. tabularcolumns:: |p{3.5cm}|p{3.5cm}|p{3.5cm}|p{6.6cm}|
89
90 .. c:type:: v4l2_dbg_match
91
92 .. flat-table:: struct v4l2_dbg_match
93 :header-rows: 0
94 :stub-columns: 0
95 :widths: 1 1 2
96
97 * - __u32
98 - ``type``
99 - See :ref:`chip-match-types` for a list of possible types.
100 * - union {
101 - (anonymous)
102 * - __u32
103 - ``addr``
104 - Match a chip by this number, interpreted according to the ``type``
105 field.
106 * - char
107 - ``name[32]``
108 - Match a chip by this name, interpreted according to the ``type``
109 field. Currently unused.
110 * - }
111 -
112
113
114 .. c:type:: v4l2_dbg_register
115
116 .. flat-table:: struct v4l2_dbg_register
117 :header-rows: 0
118 :stub-columns: 0
119
120 * - struct v4l2_dbg_match
121 - ``match``
122 - How to match the chip, see :c:type:`v4l2_dbg_match`.
123 * - __u32
124 - ``size``
125 - The register size in bytes.
126 * - __u64
127 - ``reg``
128 - A register number.
129 * - __u64
130 - ``val``
131 - The value read from, or to be written into the register.
132
133
134 .. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.5cm}|
135
136 .. _chip-match-types:
137
138 .. flat-table:: Chip Match Types
139 :header-rows: 0
140 :stub-columns: 0
141 :widths: 3 1 4
142
143 * - ``V4L2_CHIP_MATCH_BRIDGE``
144 - 0
145 - Match the nth chip on the card, zero for the bridge chip. Does not
146 match sub-devices.
147 * - ``V4L2_CHIP_MATCH_SUBDEV``
148 - 4
149 - Match the nth sub-device.
150
151 Return Value
152 ============
153
154 On success 0 is returned, on error -1 and the ``errno`` variable is set
155 appropriately. The generic error codes are described at the
156 :ref:`Generic Error Codes <gen-errors>` chapter.
157
158 EPERM
159 Insufficient permissions. Root privileges are required to execute
160 these ioctls.
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