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Date: Fri, 25 Aug 2017 15:31:27 +0200 From: Hans Verkuil <hverkuil@...all.nl> To: Mauro Carvalho Chehab <mchehab@...pensource.com>, Linux Doc Mailing List <linux-doc@...r.kernel.org>, Linux Media Mailing List <linux-media@...r.kernel.org> Cc: Mauro Carvalho Chehab <mchehab@...radead.org>, linux-kernel@...r.kernel.org, Jonathan Corbet <corbet@....net> Subject: Re: [PATCH v2 1/3] media: open.rst: better document device node naming On 25/08/17 14:52, 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 identify for a given device. > > Signed-off-by: Mauro Carvalho Chehab <mchehab@...pensource.com> > --- > Documentation/media/uapi/v4l/open.rst | 40 ++++++++++++++++++++++++++++++----- > 1 file changed, 35 insertions(+), 5 deletions(-) > > diff --git a/Documentation/media/uapi/v4l/open.rst b/Documentation/media/uapi/v4l/open.rst > index afd116edb40d..9b98d10d5153 100644 > --- a/Documentation/media/uapi/v4l/open.rst > +++ b/Documentation/media/uapi/v4l/open.rst > @@ -7,12 +7,12 @@ Opening and Closing Devices > *************************** > > > -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. > > @@ -20,8 +20,38 @@ Each driver thus loaded registers one or more device nodes with major > number 81 and a minor number between 0 and 255. Minor numbers are > allocated dynamically unless the kernel is compiled with the kernel > option CONFIG_VIDEO_FIXED_MINOR_RANGES. In that case minor numbers > -are allocated in ranges depending on the device node type (video, radio, > -etc.). > +are allocated in ranges depending on the device node type. > + > +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 add: and modulators. > +``/dev/swradioX`` Software Defined Radio tuners Ditto. > +``/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's not warranty that ``X`` will remain the same for the same "There is no" > + 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/`` that can use to uniquelly ``/dev/v4l/by-id/`` and ``/dev/v4l/by-path/`` directories containing links that be can used to uniquely > + 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 > + > > Many drivers support "video_nr", "radio_nr" or "vbi_nr" module > options to select specific video/radio/vbi node numbers. This allows the > With these changes: Acked-by: Hans Verkuil <hans.verkuil@...co.com> Thanks! Hans
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