Re: [PATCH v2 2/2] dt-bindings: drm/bridge: Document Cadence DSI bridge bindings

[Archit Taneja <architt-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org>]

On 06/19/2017 03:42 PM, Boris Brezillon wrote:
> On Tue, 13 Jun 2017 11:02:47 +0200
> Andrzej Hajda <a.hajda-Sze3O3UU22JBDgjK7y7TUQ@public.gmane.org> wrote:
> 
>> Hi,
>>
>> Just spotted this thread.
>>
>> On 06.06.2017 14:58, Tomi Valkeinen wrote:
>>> On 06/06/17 15:48, Boris Brezillon wrote:
>>>   
>>>> Okay. Thanks for the clarification. Can you confirm that this version
>>>> is correct?
>>>>
>>>>   	dsi@xxx {
>>>>   		#address-cells = <1>;
>>>>   		#size-cells = <0>;
>>>>   
>>>>   		ports {
>>>>   			#address-cells = <1>;
>>>>   			#size-cells = <0>;
>>>> 			dpi_in: port@0 {
>>>>   				reg = <0>;
>>>>   				#address-cells = <1>;
>>>>   				#size-cells = <0>;
>>>>   
>>>>   				endpoint@0 {
>>>>   					remote-endpoint = <&dpi_out>;
>>>>   				};
>>>>   			};
>>>>   
>>>>   			dsi_out: port@1 {
>>>>   				reg = <1>;
>>>> 				#address-cells = <1>;
>>>>   				#size-cells = <0>;
>>>>   
>>>>   				dsi_out_vc0: endpoint@0 {
>>>> 					reg = <0>;
>>>>   					remote-endpoint = <&dsi_panel0_in>;
>>>> 				};
>>>>
>>>>   				dsi_out_vc1: endpoint@1 {
>>>> 					reg = <1>;
>>>>   					remote-endpoint = <&dsi_panel1_in>;
>>>>   				};
>>>>   			};
>>>>   		};
>>>>   
>>>>   		panel@0 {
>>>>   			compatible = "...";
>>>>   			reg = <0>;
>>>>   			#address-cells = <1>;
>>>>   			#size-cells = <0>;
>>>>   
>>>>   			port@0 {
>>>>   				#address-cells = <1>;
>>>>   		                #size-cells = <0>;
>>>>   				reg = <0>;
>>>>   
>>>>   				dsi_panel0_in: endpoint@0 {
>>>> 					reg = <0>;
>>>>   					remote-endpoint = <&dsi_out_vc0>;
>>>>   				};
>>>>   			};
>>>>   		};
>>>>   
>>>>   		panel@1 {
>>>>   			compatible = "...";
>>>>   			reg = <1>;
>>>>   			#address-cells = <1>;
>>>>   			#size-cells = <0>;
>>>>   
>>>>   			port@0 {
>>>>   				#address-cells = <1>;
>>>>   		                #size-cells = <0>;
>>>>   				reg = <0>;
>>>>   
>>>>   				dsi_panel1_in: endpoint@0 {
>>>> 					reg = <0>;
>>>>   					remote-endpoint = <&dsi_out_vc1>;
>>>>   				};
>>>>   			};
>>>>   		};
>>>>   	};
>>>>   
>>> Looks correct to me. I think it can be a bit shorter though:
>>>
>>> - You don't need #address-cells and #size-cells for all. I think those
>>> are inherited from the parent.
>>> - If there's just one port and one endpoint, you can leave the 'reg'
>>> out, as it's considered to be 0 by default.
>>>
>>> So for the panel, you can have just:
>>>
>>> port {
>>> 	dsi_panel1_in: endpoint {
>>> 		remote-endpoint = <&dsi_out_vc1>;
>>> 	};
>>> };
>>
>> In case DSI bus is used to both control and sending video signal you can
>> skip video links from dsi-host to dsi-child, so nodes can look like:
>>
>>
>>   	dsi@xxx {
>>   		#address-cells = <1>;
>>   		#size-cells = <0>;
>>   
>>   		ports {
>>   			#address-cells = <1>;
>>   			#size-cells = <0>;
>> 			dpi_in: port@0 {
>>   				reg = <0>;
>>   				#address-cells = <1>;
>>   				#size-cells = <0>;
>>   
>>   				endpoint@0 {
>>   					remote-endpoint = <&dpi_out>;
>>   				};
>>   			};
>>   
>>   		};
>>   
>>   		panel@0 {
>>   			compatible = "...";
>>   			reg = <0>;
>>   		};
>>   
>>   		panel@1 {
>>   			compatible = "...";
>>   			reg = <1>;
>>   		};
>>   	};
>>
> 
> Does that mean I should make port1 (AKA DSI ouput port) optional?
> IMHO, it's clearer when these links are explicitly described in the DT,
> but maybe there are good reasons to keep it implicit for the "control
> through DSI" case.
> 
> Tomi, Archit, any opinion on this?

I guess there isn't any harm in having the links explicitly described. It's
just that those ports won't be used by the driver in the "control through DSI"
case.

For the MSM DSI host bindings, we actually keep the DSI 'data-lanes' param in the
DSI output port, so it's mandatory even if the panel/bridge is controlled via
the host DSI bus.

Andrzej,

Are there any reasons why keeping the host-to-child links in the "control through
DSI" case could be harmful?

Archit

> 
> Regards,
> 
> Boris
> 

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