From: Mauro Carvalho Chehab <mche...@s-opensource.com> 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 identify for a given device.
Acked-by: Hans Verkuil <hans.verk...@cisco.com> Signed-off-by: Mauro Carvalho Chehab <mchehab+sams...@kernel.org> --- Documentation/media/uapi/v4l/open.rst | 44 +++++++++++++++++++++++++-- 1 file changed, 41 insertions(+), 3 deletions(-) diff --git a/Documentation/media/uapi/v4l/open.rst b/Documentation/media/uapi/v4l/open.rst index afd116edb40d..7e7aad784388 100644 --- a/Documentation/media/uapi/v4l/open.rst +++ b/Documentation/media/uapi/v4l/open.rst @@ -7,12 +7,14 @@ 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. @@ -23,6 +25,42 @@ 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 existing V4L2 device node types are: + +======================== ====================================================== +Default device node name Usage +======================== ====================================================== +``/dev/videoX`` Video input/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 +======================== ====================================================== + +Where ``X`` is a non-negative number. + +.. 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 + + 3. **V4L2 sub-device nodes** (e. g. ``/dev/v4l-sudevX``) provide a + different API and aren't considered as V4L2 device nodes. + + They are 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 -- 2.17.1
