linux-kernel - Re: [PATCH v4 3/3] Documentation: of: Document graph bindings

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Date:	Wed, 26 Feb 2014 15:57:03 +0100
From:	Philipp Zabel <p.zabel@...gutronix.de>
To:	Tomi Valkeinen <tomi.valkeinen@...com>
Cc:	Russell King - ARM Linux <linux@....linux.org.uk>,
	Mauro Carvalho Chehab <m.chehab@...sung.com>,
	Grant Likely <grant.likely@...aro.org>,
	Rob Herring <robh+dt@...nel.org>,
	Sylwester Nawrocki <s.nawrocki@...sung.com>,
	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	Kyungmin Park <kyungmin.park@...sung.com>,
	linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
	devicetree@...r.kernel.org,
	Guennadi Liakhovetski <g.liakhovetski@....de>
Subject: Re: [PATCH v4 3/3] Documentation: of: Document graph bindings

Hi Tomi,

Am Mittwoch, den 26.02.2014, 15:14 +0200 schrieb Tomi Valkeinen:
> On 25/02/14 16:58, Philipp Zabel wrote:
> 
> > +Optional endpoint properties
> > +----------------------------
> > +
> > +- remote-endpoint: phandle to an 'endpoint' subnode of a remote device node.
> 
> Why is that optional? What use is an endpoint, if it's not connected to
> something?

This allows to include the an empty endpoint template in a SoC dtsi for
the convenience of board dts writers. Also, the same property is
currently listed as optional in video-interfaces.txt.

  soc.dtsi:
	display-controller {
		port {
			disp0: endpoint { };
		};
	};

  board.dts:
	#include "soc.dtsi"
	&disp0 {
		remote-endpoint = <&panel_input>;
	};
	panel {
		port {
			panel_in: endpoint {
				remote-endpoint = <&disp0>;
			};
		};
	};

Any board not using that port can just leave the endpoint disconnected.

On the other hand, the same could be achieved with Heiko Stübner's
conditional nodes dtc patch:

  soc.dtsi:
	display-controller {
		port {
			/delete-unreferenced/ disp0: endpoint { };
		};
	};

> Also, if this is being worked on, I'd like to propose the addition of
> simpler single-endpoint cases which I've been using with OMAP DSS. So if
> there's just a single endpoint for the device, which is very common, you
> can have just:
> 
> device {
> 	...
> 	endpoint { ... };
> };
> 
> However, I guess that the patch just keeps growing and growing, so maybe
> it's better to add such things later =).

Yes, that looks good. I'd be happy if we could add this in a second step
as a backwards compatible simplification.

regards
Philipp

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