Hi Sakari,
Em Tue, 29 Aug 2017 11:34:06 +0300
Sakari Ailus <sakari.ai...@iki.fi> escreveu:
> Hi Mauro,
>
> On Mon, Aug 28, 2017 at 09:53:56AM -0300, 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.
> >
> > Acked-by: Hans Verkuil <hans.verk...@cisco.com>
> > Signed-off-by: Mauro Carvalho Chehab <mche...@s-opensource.com>
> > ---
> > Documentation/media/uapi/v4l/open.rst | 39
> > ++++++++++++++++++++++++++++++++---
> > 1 file changed, 36 insertions(+), 3 deletions(-)
> >
> > diff --git a/Documentation/media/uapi/v4l/open.rst
> > b/Documentation/media/uapi/v4l/open.rst
> > index afd116edb40d..fc0037091814 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 +25,37 @@ 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
>
> Should we document V4L2 sub-device nodes here as well? They are implemented
> by the V4L2 core as well as the other device node types.
>
> Their purpose is somewhat different, though, and I think we'll need to make
> that explicit somehow.
Actually, what we're calling as "V4L2 Device node" are the vdev-centric
device nodes. That should not include /dev/v4l-subdevX.
What we can do here is to explicitly rule out the subdev interfaces,
with something like:
.. note::
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`.
>
> > +========================
> > ======================================================
> > +
> > +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 warranty that ``X`` will remain the same for the same
>
> s/warranty/guarantee/
OK.
>
> > + 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/`` directoiries
> > containing
>
> "directories"
OK.
>
> > + 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
> > +
> > +
> > 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
>
Thanks,
Mauro
