media/v4l/open.rst

1 .. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
12 Controlling a hardware peripheral via V4L2
15 Hardware that is supported using the V4L2 uAPI often consists of multiple
22 the hardware, which may also expose device nodes, called V4L2 sub-devices.
24 When such V4L2 sub-devices are exposed, they allow controlling those
25 other hardware components - usually connected via a serial bus (like
26 I²C, SMBus or SPI). Depending on the bridge driver, those sub-devices
27 can be controlled indirectly via the bridge driver or explicitly via
29 :ref:`V4L2 sub-devices <subdev>`.
32 :ref:`Media Controller <media_controller>` are called **MC-centric**
33 devices. The devices that are fully controlled via V4L2 device nodes
34 are called **video-node-centric**.
36 Userspace can check if a V4L2 hardware peripheral is MC-centric by
38 :ref:`device_caps field <device-capabilities>`.
41 then it is MC-centric, otherwise, it is video-node-centric.
43 It is required for MC-centric drivers to identify the V4L2
44 sub-devices and to configure the pipelines via the
46 Also, the sub-devices' configuration shall be controlled via the
47 :ref:`sub-device API <subdev>`.
51    A video-node-centric may still provide media-controller and
52    sub-device interfaces as well.
54   However, in that case the media-controller and the sub-device
55   interfaces are read-only and just provide information about the
84 ``/dev/v4l-touchX``	 Touch sensors
85 ``/dev/v4l-subdevX``	 Video sub-devices (used by sensors and other
86 			 components of the hardware peripheral)\ [#]_
89 Where ``X`` is a non-negative integer.
93    1. The actual device node name is system-dependent, as udev rules may apply.
97       ``/dev/v4l/by-id/`` and ``/dev/v4l/by-path/`` directories containing
102 	├── by-id
103 	│   └── usb-OmniVision._USB_Camera-B4.04.27.1-video-index0 -> ../../video0
104 	└── by-path
105 	    └── pci-0000:00:14.0-usb-0:2:1.0-video-index0 -> ../../video0
107 .. [#] **V4L2 sub-device nodes** (e. g. ``/dev/v4l-subdevX``) use a different
117 .. code-block:: none
164 Besides video input or output the hardware may also support audio
170 hardware use the Media Controller (see :ref:`media_controller`) which can
174 `v4l-utils <http://git.linuxtv.org/cgit.cgi/v4l-utils.git/>`__ git
176 towards both Media Controller-based devices and devices that do not use
178 linux-media mailing list:
206 the priority mechanism described in :ref:`app-pri`.
222 :ref:`ioctl() <func-ioctl>` function as explained in the following