On Wed, Jan 12, 2022 at 12:01:52AM +0530, Jagan Teki wrote:
> Some OF graphs don't require 'port' or 'ports' to represent the
> downstream panel or bridge; instead it simply adds a child node
> on a given parent node.

All bindings using OF graph nodes require either port or ports.

DSI Host however don't have to use the OF graph, and that's what you're
talking about.

> drm_of_find_panel_or_bridge can lookup panel or bridge for a given
> node based on the OF graph port and endpoint and it fails to use
> if the given node has a child panel or bridge.
> 
> This patch add support to lookup that given node has child panel
> or bridge however that child node is neither a 'port' nor a 'ports'
> node.
> 
> Example OF graph representation of DSI host, which has 'port'
> but not has 'ports' and has child panel node.
> 
> dsi {
> 	compatible = "allwinner,sun6i-a31-mipi-dsi";
> 	#address-cells = <1>;
> 	#size-cells = <0>;
> 
> 	port {
> 		dsi_in_tcon0: endpoint {
> 			remote-endpoint = <tcon0_out_dsi>;
> 	};
> 
> 	panel@0 {
> 		reg = <0>;
> 	};
> };
> 
> Example OF graph representation of DSI host, which has 'ports'
> but not has 'port' and has child panel node.
> 
> dsi {
>         compatible = "samsung,exynos5433-mipi-dsi";
>         #address-cells = <1>;
>         #size-cells = <0>;
> 
> 	ports {
> 		#address-cells = <1>;
> 		#size-cells = <0>;
> 
> 		port@0 {
> 			reg = <0>;
> 
>                 	dsi_to_mic: endpoint {
>                         	remote-endpoint = <&mic_to_dsi>;
>                 	};
>                 };
>         };
>
>         panel@0 {
>                 reg = <0>;
>         };
> };

I can't see how that one makes sense. The endpoint seems to have a
single output, yet you also have a panel under it which is also an
output? You should have at least the virtual channel of that endpoint
somewhere to differentiate data between the panel and whatever is
connected on the other side of that endpoint.

> Example OF graph representation of DSI host, which has neither
> a 'port' nor a 'ports' but has child panel node.
> 
> dsi0 {
> 	compatible = "ste,mcde-dsi";
> 	#address-cells = <1>;
> 	#size-cells = <0>;
> 
> 	panel@0 {
> 		reg = <0>;
> 	};
> };
> 
> Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
> ---
> Changes for v3:
> - updated based on other usecase where 'ports' used along with child
> Changes for v2:
> - drop of helper
> https://patchwork.kernel.org/project/dri-devel/cover/20211207054747.461029-1-jagan@amarulasolutions.com/
> - support 'port' alone OF graph
> - updated comments
> - added simple code
> 
>  drivers/gpu/drm/drm_of.c | 18 ++++++++++++++++++
>  1 file changed, 18 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_of.c b/drivers/gpu/drm/drm_of.c
> index 59d368ea006b..aeddd39b8df6 100644
> --- a/drivers/gpu/drm/drm_of.c
> +++ b/drivers/gpu/drm/drm_of.c
> @@ -249,6 +249,22 @@ int drm_of_find_panel_or_bridge(const struct device_node *np,
>  	if (panel)
>  		*panel = NULL;
>  
> +	/**
> +	 * Some OF graphs don't require 'port' or 'ports' to represent the
> +	 * downstream panel or bridge; instead it simply adds a child node
> +	 * on a given parent node.

All OF graphs require either port or ports. DSI hosts can just have a
child node.

Maxime