Re: [PATCH RFC v2] media: open.rst: document devnode-centric and mc-centric types

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Hans,

On Friday, 25 August 2017 11:59:40 EEST Hans Verkuil wrote:
> On 24/08/17 14:07, Mauro Carvalho Chehab wrote:
> > From: "mchehab@s-opensource.com" <mchehab@s-opensource.com>
> > 
> > When we added support for omap3, back in 2010, we added a new
> > type of V4L2 devices that aren't fully controlled via the V4L2
> > device node. Yet, we never made it clear, at the V4L2 spec,
> > about the differences between both types.
> > 
> > Let's document them with the current implementation.
> > 
> > Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
> > Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>
> > ---
> > 
> >  Documentation/media/uapi/v4l/open.rst | 47 ++++++++++++++++++++++++++++++
> >  1 file changed, 47 insertions(+)
> > 
> > diff --git a/Documentation/media/uapi/v4l/open.rst
> > b/Documentation/media/uapi/v4l/open.rst index afd116edb40d..cf522d9bb53c
> > 100644
> > --- a/Documentation/media/uapi/v4l/open.rst
> > +++ b/Documentation/media/uapi/v4l/open.rst
> > @@ -6,6 +6,53 @@
> > 
> >  Opening and Closing Devices
> >  ***************************
> > 
> > +Types of V4L2 device control
> 
> I don't like calling this 'device control'. Mostly because the word 'device'
> can mean almost anything and is very overused.
> 
> How about "hardware control"?

The word device is used for different purposes that make the text unclear in 
my opinion. We have at least three different kinds of devices:

- device node
- kernel struct device (fortunately not relevant to the V4L2 API discussion)
- hardware counterpart of the kernel struct device (SoC IP core, I2C chip, 
...)
- group of hardware devices that together make a larger user-facing functional 
device (for instance the SoC ISP IP cores and external camera sensors together 
make a camera device)

We need different terms for those different concepts, and we need to be very 
consistent in our usage of those terms. I believe we should also define them 
formally at the beginning of the documentation to avoid confusion.

[snip]

-- 
Regards,

Laurent Pinchart