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

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Date:	Thu, 27 Feb 2014 11:52:36 +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 Donnerstag, den 27.02.2014, 10:08 +0200 schrieb Tomi Valkeinen:
> On 26/02/14 17:47, Philipp Zabel wrote:
> > Please let's not make it mandatory for a port node to contain an
> > endpoint. For any device with multiple ports we can't use the simplified
> > form above, and only adding the (correctly numbered) port in all the
> > board device trees would be a pain.
> 
> That's true. I went with having the ports in the board file, for example
> on omap3 the dss has two ports, and N900 board uses the second one:
> 
> &dss {
> 	status = "ok";
> 
> 	pinctrl-names = "default";
> 	pinctrl-0 = <&dss_sdi_pins>;
> 
> 	vdds_sdi-supply = <&vaux1>;
> 
> 	ports {
> 		#address-cells = <1>;
> 		#size-cells = <0>;
> 
> 		port@1 {
> 			reg = <1>;
> 
> 			sdi_out: endpoint {
> 				remote-endpoint = <&lcd_in>;
> 				datapairs = <2>;
> 			};
> 		};
> 	};
> };

This is a bit verbose, and if your output port is on an encoder device
with multiple inputs, the correct port number would become a bit
unintuitive. For example, we'd have to use port@4 as the output encoder
units that have a 4-port input multiplexer and port@1 for those that
don't.

> Here I guess I could have:
> 
> &dss {
> 	status = "ok";
> 
> 	pinctrl-names = "default";
> 	pinctrl-0 = <&dss_sdi_pins>;
> 
> 	vdds_sdi-supply = <&vaux1>;
> };

What is supplied by this regulator. Is it the PHY?

> &dss_sdi_port {
> 	sdi_out: endpoint {
> 		remote-endpoint = <&lcd_in>;
> 		datapairs = <2>;
> 	};
> };
> 
> But I didn't like that as it splits the pincontrol and regulator supply
> from the port/endpoint, which are functionally linked together.
>
> Actually, somewhat aside the subject, I'd like to have the pinctrl and
> maybe regulator supply also per endpoint, but I didn't see how that
> would be possible with the current framework. If a board would need to
> endpoints for the same port, most likely it would also need to different
> sets of pinctrls.

I have a usecase for this the other way around. The i.MX6 DISP0 parallel
display pads can be connected to two different display controllers via
multiplexers in the pin control block.

parallel-display {
	compatible = "fsl,imx-parallel-display";
	#address-cells = <1>;
	#size-cells = <0>;

	port@0 {
		endpoint {
			remote-endpoint = <&ipu1_di0>;
		};
	};

	port@1 {
		endpoint {
			remote-endpoint = <&ipu2_di0>;
		};
	};

	disp0: port@2 {
		endpoint {
			pinctrl-names = "0", "1";
			pinctrl-0 = <&pinctrl_disp0_ipu1>;
			pinctrl-1 = <&pinctrl_disp0_ipu2>;
			remote-endpoint = <&lcd_in>;
		};
	}
};

Here, depending on the active input port, the corresponding pin control
on the output port could be set. This is probably quite driver specific,
so I don't see yet how the framework should help with this. In any case,
maybe this is a bit out of scope for the generic graph bindings.

regards
Philipp

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