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Date:	Fri, 21 Mar 2014 10:20:51 +0200
From:	Tomi Valkeinen <tomi.valkeinen@...com>
To:	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	Russell King - ARM Linux <linux@....linux.org.uk>
CC:	Mauro Carvalho Chehab <m.chehab@...sung.com>,
	Grant Likely <grant.likely@...aro.org>,
	Philipp Zabel <p.zabel@...gutronix.de>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Rob Herring <robherring2@...il.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

On 20/03/14 20:49, Laurent Pinchart wrote:

>> The CPU is the _controlling_ component - it's the component that has to
>> configure the peripherals so they all talk to each other in the right
>> way.  Therefore, the view of it needs to be CPU centric.
>>
>> If we were providing a DT description for consumption by some other
>> device in the system, then the view should be as seen from that device
>> instead.
>>
>> Think about this.  Would you describe a system starting at, say, the
>> system keyboard, and branching all the way through just becuase that's
>> how you interact with it, or would you describe it from the CPUs point
>> of view because that's what has to be in control of the system.
> 
> DT has been designed to represent a control-based view of the system. It does 
> so pretty well using its tree-based model. However, it doesn't have a native 
> way to represent a flow-based graph, hence the OF graph solution we're 
> discussing. The whole point of this proposal is to represent the topology of 
> the media device, not how each entity is controlled.

I agree with Laurent here. I think this is an important point to keep in
mind. We already describe the control graph in the DT via the
parent-child relationships. There's no point in describing the same
thing again with the graph links being discussed.

 Tomi



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