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

[Steve Longerbeam]

On 03/11/2017 10:59 AM, Russell King - ARM Linux wrote:
> On Sat, Mar 11, 2017 at 10:54:55AM -0800, Steve Longerbeam wrote:
> > On 03/11/2017 10:45 AM, Russell King - ARM Linux wrote:
> > > I really don't think expecting the user to understand and configure
> > > the pipeline is a sane way forward.  Think about it - should the
> > > user need to know that, because they have a bayer-only CSI data
> > > source, that there is only one path possible, and if they try to
> > > configure a different path, then things will just error out?
> > >
> > > For the case of imx219 connected to iMX6, it really is as simple as
> > > "there is only one possible path" and all the complexity of the media
> > > interfaces/subdevs is completely unnecessary.  Every other block in
> > > the graph is just noise.
> > >
> > > The fact is that these dot graphs show a complex picture, but reality
> > > is somewhat different - there's only relatively few paths available
> > > depending on the connected source and the rest of the paths are
> > > completely useless.
> >
> > I totally disagree there. Raw bayer requires passthrough yes, but for
> > all other media bus formats on a mipi csi-2 bus, and all other media
> > bus formats on 8-bit parallel buses, the conersion pipelines can be
> > used for scaling, CSC, rotation, and motion-compensated de-interlacing.
>
> ... which only makes sense _if_ your source can produce those formats.
> We don't actually disagree on that.

...and there are lots of those sources! You should try getting out of
your imx219 shell some time, and have a look around! :)

> Let me re-state.  If the source can _only_ produce bayer, then there is
> _only_ _one_ possible path, and all the overhead of the media controller
> stuff is totally unnecessary.
>
> Or, are you going to tell me that the user should have the right to
> configure paths through the iMX6 hardware that are not permitted by the
> iMX6 manuals for the data format being produced by the sensor?

Anyway, no the user is not allowed to configure a path that is not
allowed by the hardware, such as attempting to pass raw bayer through
an Image Converter path.

I guess you are simply commenting that for users of bayer sensors, the
other pipelines can be "confusing". But I trust you're not saying those
other pipelines should therefore not be present, which would be a
completely nutty argument.

Steve