Re: [PATCH v4 14/36] [media] v4l2-mc: add a function to inherit controls from a pipeline

From: Mauro Carvalho Chehab
Date: Fri Mar 10 2017 - 10:54:11 EST

Em Fri, 10 Mar 2017 15:20:48 +0100
Hans Verkuil <hverkuil@xxxxxxxxx> escreveu:

> > As I've already mentioned, from talking about this with Mauro, it seems
> > Mauro is in agreement with permitting the control inheritence... I wish
> > Mauro would comment for himself, as I can't quote our private discussion
> > on the subject.
> I can't comment either, not having seen his mail and reasoning.

The rationale is that we should support the simplest use cases first.

In the case of the first MC-based driver (and several subsequent
ones), the simplest use case required MC, as it was meant to suport
a custom-made sophisticated application that required fine control
on each component of the pipeline and to allow their advanced
proprietary AAA userspace-based algorithms to work.

That's not true, for example, for the UVC driver. There, MC
is optional, as it should be.

> > Right now, my view is that v4l2 is currently being screwed up by people
> > with different opinions - there is no unified concensus on how any of
> > this stuff is supposed to work, everyone is pulling in different
> > directions. That needs solving _really_ quickly, so I suggest that
> > v4l2 people urgently talk to each other and thrash out some of the
> > issues that Steve's patch set has brought up, and settle on a way
> > forward, rather than what is seemingly happening today - which is
> > everyone working in isolation of everyone else with their own bias on
> > how things should be done.
> The simple fact is that to my knowledge no other MC applications inherit
> controls from subdevs. Suddenly doing something different here seems very
> wrong to me and needs very good reasons.

That's because it was not needed before, as other subdev-based drivers
are meant to be used only on complex scenarios with custom-made apps.