Right now, only kAPI documentation describes the device naming. However, such description is needed at the uAPI too. Add it, and describe how to get an unique identifier for a given device. Acked-by: Hans Verkuil <hans.verkuil@xxxxxxxxx> Reviewed-by: Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxx> Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@xxxxxxxxxx> --- .../userspace-api/media/v4l/open.rst | 43 +++++++++++++++++-- 1 file changed, 40 insertions(+), 3 deletions(-) diff --git a/Documentation/userspace-api/media/v4l/open.rst b/Documentation/userspace-api/media/v4l/open.rst index 38046ef20141..7f1ff8a77059 100644 --- a/Documentation/userspace-api/media/v4l/open.rst +++ b/Documentation/userspace-api/media/v4l/open.rst @@ -14,12 +14,14 @@ Opening and Closing Devices *************************** -Device Naming -============= +.. _v4l2_device_naming: + +V4L2 Device Node Naming +======================= V4L2 drivers are implemented as kernel modules, loaded manually by the system administrator or automatically when a device is first discovered. -The driver modules plug into the "videodev" kernel module. It provides +The driver modules plug into the ``videodev`` kernel module. It provides helper functions and a common application interface specified in this document. @@ -30,6 +32,41 @@ option CONFIG_VIDEO_FIXED_MINOR_RANGES. In that case minor numbers are allocated in ranges depending on the device node type (video, radio, etc.). +The device nodes supported by the Video4Linux subsystem are: + +======================== ==================================================== +Default device node name Usage +======================== ==================================================== +``/dev/videoX`` Video and metadata for capture/output devices +``/dev/vbiX`` Vertical blank data (i.e. closed captions, teletext) +``/dev/radioX`` Radio tuners and modulators +``/dev/swradioX`` Software Defined Radio tuners and modulators +``/dev/v4l-touchX`` Touch sensors +``/dev/v4l-subdevX`` Video sub-devices (used by sensors and other + components of the hardware peripheral)\ [#]_ +======================== ==================================================== + +Where ``X`` is a non-negative integer. + +.. note:: + + 1. The actual device node name is system-dependent, as udev rules may apply. + 2. There is no guarantee that ``X`` will remain the same for the same + device, as the number depends on the device driver's probe order. + If you need an unique name, udev default rules produce + ``/dev/v4l/by-id/`` and ``/dev/v4l/by-path/`` directories containing + links that can be used uniquely to identify a V4L2 device node:: + + $ tree /dev/v4l + /dev/v4l + ├── by-id + │ └── usb-OmniVision._USB_Camera-B4.04.27.1-video-index0 -> ../../video0 + └── by-path + └── pci-0000:00:14.0-usb-0:2:1.0-video-index0 -> ../../video0 + +.. [#] **V4L2 sub-device nodes** (e. g. ``/dev/v4l-subdevX``) use a different + set of system calls, as covered at :ref:`subdev`. + Many drivers support "video_nr", "radio_nr" or "vbi_nr" module options to select specific video/radio/vbi node numbers. This allows the user to request that the device node is named e.g. /dev/video5 instead -- 2.26.2
