STM32MP157 Device Tree ltdc port endpoint reg 0 vs reg 1

[petero]

Hi.

Some examples use ltdc_ep0_out / reg 0, while others use ltdc_ep1_out / reg 1.

e.g.

https://community.st.com/s/question/0D50X0000BG0RAWSQ3/stm32mp1-ltdc-device-tree-for-rgb-display

Where can I find more details on when to use reg 0 vs reg 1?

&ltdc {
	port {
		ltdc_ep1_out: endpoint@1 {
			reg = <1>;
			remote-endpoint = <&panel_rgb_in>;
		};
	};
};

Thank you

-- Peter

[Erwan SZYMANSKI]

Hello @petero​ ,

Referring to the documentation (Documentation/devicetree/bindings/display/st,stm32-ltdc.yaml), you can find this information:

********************************************************

port:

$ref: /schemas/graph.yaml#/properties/port

description: |

Video port for DPI RGB output.

ltdc has one video port with up to 2 endpoints:

- for external dpi rgb panel or bridge, using gpios

- for internal dpi input of the MIPI DSI host controller

Note: These 2 endpoints cannot be activated simultaneously.

********************************************************

 It seems that the number linked with the endpoint has no impact on the DT, that is not the case with DSI for example.

Erwan.

[Erwan SZYMANSKI]

@petero​ ,

As a comparison, if the number of the port/endpoint has an impact, you will see the following thing in the yaml (example of Documentation/devicetree/bindings/display/st,stm32-dsi.yaml):

***************************************

ports:

$ref: /schemas/graph.yaml#/properties/ports

properties:

port@0:

$ref: /schemas/graph.yaml#/properties/port

description:

DSI input port node, connected to the ltdc rgb output port.

port@1:

$ref: /schemas/graph.yaml#/properties/port

description:

DSI output port node, connected to a panel or a bridge input port"

***************************************

Kind regards,

Erwan.