On 08/05/2020 15:35, Mauro Carvalho Chehab wrote: > Em Fri, 8 May 2020 15:24:33 +0200 > Hans Verkuil <hverkuil-cisco@xxxxxxxxx> escreveu: > >> On 08/05/2020 15:10, 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. >> >> identifier >> >>> >>> Acked-by: Hans Verkuil <hans.verkuil@xxxxxxxxx> >>> 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..86816b247a17 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 input/output devices >> >> Also metadata input/output devices. >> >> I would prefer capture/output given the traditional names that V4L2 uses. >> >>> +``/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-sudevX`` Video sub-devices (used by sensors and other I2C >> >> sudevX -> subdevX >> >> You made this typo in more places, it's best to search and replace. >> >>> + devices)\ [#]_ >> >> That suggests that subdevs are i2c devices, they can be any processing block on >> any bus. > > For all the above: Ok. Will address at the next version. > > >> >>> +======================== ====================================================== >>> + >>> +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 >>> + >>> +.. [#] **V4L2 sub-device nodes** (e. g. ``/dev/v4l-sudevX``) 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 >> >> It looks like there is a missing period at the end of the sentence. > > The full sentence here is: > > 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 > of leaving it to chance. When the driver supports multiple devices of > the same type more than one device node number can be assigned, > separated by commas: > > This paragraph (untouched by this patch) sounds ok to me ;-) Ah yes, I misread the patch. It looked like there was an empty line after 'instead'. Never mind :-) Regards, Hans > > Thanks, > Mauro >
