linux-kernel - Re: [PATCH 2/4] dt-bindings: Document the Raspberry Pi Touchscreen nodes.

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Date:   Thu, 18 May 2017 17:55:25 +0300
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Archit Taneja <architt@...eaurora.org>
Cc:     Eric Anholt <eric@...olt.net>, Rob Herring <robh+dt@...nel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Mark Rutland <mark.rutland@....com>,
        Andrzej Hajda <a.hajda@...sung.com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/4] dt-bindings: Document the Raspberry Pi Touchscreen nodes.

Hi Archit,

On Thursday 18 May 2017 13:56:19 Archit Taneja wrote:
> On 05/17/2017 12:16 AM, Eric Anholt wrote:

[snip]

> > In terms of physical connections:
> >    [15-pin "DSI" connector on 2835]
> >    
> >     | I2C               | DSI
> >    
> >    / \        SPI       |
> > 
> > [TS]  [Atmel]------[TC358762]
> > 
> >        \                |
> >        
> >         \PWM            |
> >         
> >          \              | DPI
> > 
> > [some backlight]------[some unknown panel]
> > 
> > The binding I'm trying to create is to expose what's necessary for a
> > driver that talks I2C to the Atmel, which then controls the PWM and does
> > the command sequence over SPI to the Toshiba that sets up its end of the
> > DSI link.
> 
> The bridge (Atmel + TC358762 combination) here looks like it's primarily
> an i2c device (i.e, the control bus is i2c). Therefore, the drm-bridge
> driver here should be an i2c driver instead of a mipi_dsi_driver.

Glad to see we agree, that's what I've proposed in a separate answer :-) I'd 
go one step further though, there should be no DRM bridge, just a DRM panel.

> We have the facility to create a mipi DSI device without the need to have
> a corresponding node in DT. The ADV7533 and TC358767 drivers are examples
> of that.
> 
> The following is what the binding could look like, it's same as what Rob
> also mentioned previously in the thread.
> 
> Thanks,
> Archit
> 
> dsi1: dsi@...00000 {
> 	#address-cells = <1>;
> 	#size-cells = <0>;
> 	<...>
> 
> 	/* The SoC's DSI input/output port */
> 	ports {
> 		#address-cells = <1>;
> 		#size-cells = <0>;
> 
> 		/* port@0 if needed */
> 
> 		port@1 {
> 			dsi_out_port: endpoint {
> 				reg = <1>;
> 				remote-endpoint = <&bridge_dsi_port>;
> 			};
> 		};
> 	};
> };
> 
> i2c_dsi: i2c {
> 	compatible = "i2c-gpio";
> 	#address-cells = <1>;
> 	#size-cells = <0>;
> 	gpios = <&gpio 28 0
> 		 &gpio 29 0>;
> 
> 	/* the Atmel + TC35872 bridge */
> 	pitouchscreen_bridge: bridge@45 {

This should thus be lcd@45.

> 		compatible = "raspberrypi,touchscreen-bridge";

And this raspberrypi,7inch-touchscreen-panel. Shame we haven't standardized 
the vendor name prefix to rpi :-/

> 		reg = <0x45>;
> 
> 		ports {
> 			#address-cells = <1>;
> 			#size-cells = <0>;
> 
> 			port@0 {
> 				reg = <0>;
> 				bridge_dsi_port: endpoint {

This should be named panel_dsi_port.

> 					remote-endpoint = <&dsi_out_port>;
> 				};
> 			};
> 			port@1 {
> 				reg = <1>;
> 				bridge_dpi_port: endpoint {
> 					remote-endpoint = 
<&pitouchscreen_panel_port>;
> 				};
> 			};

The second port is thus not needed.

> 		};

So we can simplify this to

		port {
			panel_dsi_port: endpoint {
				remote-endpoint = <&dsi_out_port>;
			};
		};

(no need for a ports node when there's a single port)

> 	};
> };
> 
> lcd {
> 	compatible = "raspberrypi,7inch-touchscreen-panel";
> 	ports {
> 		#address-cells = <1>;
> 		#size-cells = <0>;
> 		port@0 {
> 			reg = <0>;
> 			pitouchscreen_panel_port: endpoint {
> 				remote-endpoint = <&bridge_dpi_port>;
> 			};
> 		};
> 	};
> };

And this node can go away.

-- 
Regards,

Laurent Pinchart