Hi Mauro, Thanks for working on this!
On Thu, Aug 27, 2020 at 09:21:45AM +0200, Mauro Carvalho Chehab wrote: > 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 <[email protected]> > Signed-off-by: Mauro Carvalho Chehab <[email protected]> > --- > .../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..332763053292 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 number. s/number/integer/ Reviewed-by: Sakari Ailus <[email protected]> > + > +.. 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 > -- Sakari Ailus
