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

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Message-Id: <20140308122532.1AED9C40612@trevor.secretlab.ca>
Date:	Sat, 08 Mar 2014 12:25:32 +0000
From:	Grant Likely <grant.likely@...aro.org>
To:	Tomi Valkeinen <tomi.valkeinen@...com>,
	Philipp Zabel <p.zabel@...gutronix.de>
Cc:	Russell King - ARM Linux <linux@....linux.org.uk>,
	Mauro Carvalho Chehab <m.chehab@...sung.com>,
	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

On Sat, 8 Mar 2014 11:35:38 +0200, Tomi Valkeinen <tomi.valkeinen@...com> wrote:
> On 07/03/14 20:11, Grant Likely wrote:
> 
> >>> Any board not using that port can just leave the endpoint disconnected.
> >>
> >> Hmm I see. I'm against that.
> >>
> >> I think the SoC dtsi should not contain endpoint node, or even port node
> >> (at least usually). It doesn't know how many endpoints, if any, a
> >> particular board has. That part should be up to the board dts.
> > 
> > Why? We have established precedence for unused devices still being in
> > the tree. I really see no issue with it.
> 
> I'm fine with having ports defined in the SoC dtsi. A port is a physical
> thing, a group of pins, for example.
> 
> But an endpoint is a description of the other end of a link. To me, a
> single endpoint makes no sense, there has to be a pair of endpoints. The
> board may need 0 to n endpoints, and the SoC dtsi cannot know how many
> are needed.
> 
> If the SoC dtsi defines a single endpoint for a port, and the board
> needs to use two endpoints for that port, it gets really messy: one
> endpoint is defined in the SoC dtsi, and used in the board dts. The
> second endpoint for the same port needs to be defined separately in the
> board file. I.e. something like:

Sure. If endpoints are logical, then only create the ones actually
hooked up. No problem there. But nor do I see any issue with having
empty connections if the board author things it makes sense to have them
in the dtsi.

> 
> /* the first ep */
> &port1_ep {
> 	remote-endpoint = <&..>;
> };
> 
> &port1 {
> 	/* the second ep */
> 	endpoint@2 {
> 		remote-endpoint = <&..>;
> 	};
> };
> 
> Versus:
> 
> &port1 {
> 	/* the first ep */
> 	endpoint@1 {
> 		remote-endpoint = <&..>;
> 	};
> 
> 	/* the second ep */
> 	endpoint@2 {
> 		remote-endpoint = <&..>;
> 	};
> };
> 
>  Tomi
> 
> 

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