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

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Date:   Sun, 26 Mar 2017 11:12:57 +0200
From:   Pavel Machek <pavel@....cz>
To:     Mauro Carvalho Chehab <mchehab@...pensource.com>
Cc:     Steve Longerbeam <slongerbeam@...il.com>,
        Russell King - ARM Linux <linux@...linux.org.uk>,
        mark.rutland@....com, andrew-ct.chen@...iatek.com,
        minghsiu.tsai@...iatek.com, nick@...anahar.org,
        songjun.wu@...rochip.com, Hans Verkuil <hverkuil@...all.nl>,
        shuah@...nel.org, devel@...verdev.osuosl.org,
        markus.heiser@...marIT.de,
        laurent.pinchart+renesas@...asonboard.com, robert.jarzmik@...e.fr,
        geert@...ux-m68k.org, p.zabel@...gutronix.de,
        linux-media@...r.kernel.org, devicetree@...r.kernel.org,
        kernel@...gutronix.de, arnd@...db.de, tiffany.lin@...iatek.com,
        bparrot@...com, robh+dt@...nel.org, horms+renesas@...ge.net.au,
        mchehab@...nel.org, linux-arm-kernel@...ts.infradead.org,
        niklas.soderlund+renesas@...natech.se, gregkh@...uxfoundation.org,
        linux-kernel@...r.kernel.org, Sakari Ailus <sakari.ailus@....fi>,
        jean-christophe.trotin@...com, sakari.ailus@...ux.intel.com,
        fabio.estevam@....com, shawnguo@...nel.org,
        sudipm.mukherjee@...il.com
Subject: script to setup pipeline was Re: [PATCH v4 14/36] [media] v4l2-mc:
 add a function to inherit controls from a pipeline

Hi!

> > I do agree with you that MC places a lot of burden on the user to
> > attain a lot of knowledge of the system's architecture.
> 
> Setting up the pipeline is not the hard part. One could write a
> script to do that. 

Can you try to write that script? I believe it would solve big part of
the problem.

> > And my other point is, I think most people who have a need to work with
> > the media framework on a particular platform will likely already be
> > quite familiar with that platform.
> 
> I disagree. The most popular platform device currently is Raspberry PI.
> 
> I doubt that almost all owners of RPi + camera module know anything
> about MC. They just use Raspberry's official driver with just provides
> the V4L2 interface.
> 
> I have a strong opinion that, for hardware like RPi, just the V4L2
> API is enough for more than 90% of the cases.

Maybe V4L2 API is enough for 90% of the users. But I don't believe
that means that we should provide compatibility. V4L2 API is not good
enough for complex devices, and if we can make RPi people fix
userspace... that's a good thing.

> > The media graph for imx6 is fairly self-explanatory in my opinion.
> > Yes that graph has to be generated, but just with a simple 'media-ctl
> > --print-dot', I don't see how that is difficult for the user.
> 
> Again, IMHO, the problem is not how to setup the pipeline, but, instead,
> the need to forward controls to the subdevices.
> 
> To use a camera, the user needs to set up a set of controls for the
> image to make sense (bright, contrast, focus, etc). If the driver
> doesn't forward those controls to the subdevs, an application like
> "camorama" won't actually work for real, as the user won't be able
> to adjust those parameters via GUI.

I believe this can be fixed in libv4l2.
								Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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