linux-kernel - Re: [RFC PATCH] [media]: of: move graph helpers from drivers/media/v4l2-core to drivers/of

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Message-ID: <13435143.OQHHLITVrH@avalon>
Date:	Thu, 20 Mar 2014 19:50:35 +0100
From:	Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	Grant Likely <grant.likely@...aro.org>,
	Tomi Valkeinen <tomi.valkeinen@...com>,
	Philipp Zabel <p.zabel@...gutronix.de>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Rob Herring <robherring2@...il.com>,
	Mauro Carvalho Chehab <m.chehab@...sung.com>,
	Rob Herring <robh+dt@...nel.org>,
	Sylwester Nawrocki <s.nawrocki@...sung.com>,
	Kyungmin Park <kyungmin.park@...sung.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Philipp Zabel <philipp.zabel@...il.com>
Subject: Re: [RFC PATCH] [media]: of: move graph helpers from drivers/media/v4l2-core to drivers/of

Hi Russell,

On Thursday 20 March 2014 18:18:20 Russell King - ARM Linux wrote:
> On Thu, Mar 20, 2014 at 07:16:29PM +0100, Laurent Pinchart wrote:
> > On Thursday 20 March 2014 17:54:31 Grant Likely wrote:
> > > On Wed, 12 Mar 2014 10:25:56 +0000, Russell King - ARM Linux wrote:

[snip]

> > > > I believe trying to do this according to the flow of data is just
> > > > wrong. You should always describe things from the primary device for
> > > > the CPU towards the peripheral devices and never the opposite
> > > > direction.
> > > 
> > > Agreed.
> > 
> > Absolutely not agreed. The whole concept of CPU towards peripherals only
> > makes sense for very simple devices and breaks as soon as the hardware
> > gets more complex. There's no such thing as CPU towards peripherals when
> > peripherals communicate directly.
> > 
> > Please consider use cases more complex than just a display controller and
> > an encoder, and you'll realize how messy not being able to parse the
> > whole graph at once will become. Let's try to improve things, not to make
> > sure to prevent support for future devices.
> 
> That's odd, I did.
> 
> Please draw some (ascii) diagrams of the situations you're saying this
> won't work for, because at the moment all I'm seeing is some vague
> hand-waving rather than anything factual that I can relate to.  Help
> us to actually _see_ the problem you have with this approach so we can
> understand it.

Working on it. Given my drawing skills this will take a bit of time.

-- 
Regards,

Laurent Pinchart

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