[PATCH v2] drm: of: Lookup if child node has panel or bridge

[Jagan Teki <jagan@xxxxxxxxxxxxxxxxxxxx>]

Some OF graphs don't require 'ports' to represent the
downstream panel or bridge; instead it simply adds a child
node on a given parent node.

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 cannot be a 'port'
alone or it cannot be a 'port' node too.

Example OF graph representation of DSI host, which doesn't
have 'ports' and has child panel.

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 doesn't
have 'ports' and has child bridge.

dsi {
	compatible = "allwinner,sun6i-a31-mipi-dsi";
	#address-cells = <1>;
	#size-cells = <0>;

	port {
		dsi_in_tcon0: endpoint {
			remote-endpoint = <tcon0_out_dsi>;
	};

	bridge@0 {
		reg = <0>;

		ports {
			#address-cells = <1>;
			#size-cells = <0>;

			bridge_out: port@1 {
				reg = <1>;

				bridge_out_panel: endpoint {
					remote-endpoint = <&panel_out_bridge>;
				};
			};
		};
	};
};

Example OF graph representation of DSI host, which doesn't
have 'ports' or 'port' and has child panel.

dsi0 {
	compatible = "ste,mcde-dsi";
	#address-cells = <1>;
	#size-cells = <0>;

	panel@0 {
		reg = <0>;
	};
};

Example OF graph representation of LTDC host, which doesn't
have 'ports' or child panel/bridge and has 'port'.

ltdc {
	compatible = "st,stm32-ltdc";
	#address-cells = <1>;
	#size-cells = <0>;

	port {
	};
};

Signed-off-by: Jagan Teki <jagan@xxxxxxxxxxxxxxxxxxxx>
---
Changes for v2:
- drop of helper
https://patchwork.kernel.org/project/dri-devel/cover/20211207054747.461029-1-jagan@xxxxxxxxxxxxxxxxxxxx/
- support 'port' alone OF graph
- updated comments
- added simple code

 drivers/gpu/drm/drm_of.c | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/drivers/gpu/drm/drm_of.c b/drivers/gpu/drm/drm_of.c
index 59d368ea006b..7d018ff8bc83 100644
--- a/drivers/gpu/drm/drm_of.c
+++ b/drivers/gpu/drm/drm_of.c
@@ -249,6 +249,27 @@ int drm_of_find_panel_or_bridge(const struct device_node *np,
 	if (panel)
 		*panel = NULL;
 
+	/**
+	 * Some OF graphs don't require 'ports' to represent the downstream
+	 * panel or bridge; instead it simply adds a child node on a given
+	 * parent node.
+	 *
+	 * Lookup that child node for a given parent however that child
+	 * cannot be a 'port' alone or it cannot be a 'port' node too.
+	 */
+	if (!of_get_child_by_name(np, "ports")) {
+		if (of_get_child_by_name(np, "port") && (of_get_child_count(np) == 1))
+			goto of_graph_get_remote;
+
+		for_each_available_child_of_node(np, remote) {
+			if (of_node_name_eq(remote, "port"))
+				continue;
+
+			goto of_find_panel_or_bridge;
+		}
+	}
+
+of_graph_get_remote:
 	/*
 	 * of_graph_get_remote_node() produces a noisy error message if port
 	 * node isn't found and the absence of the port is a legit case here,
@@ -259,6 +280,8 @@ int drm_of_find_panel_or_bridge(const struct device_node *np,
 		return -ENODEV;
 
 	remote = of_graph_get_remote_node(np, port, endpoint);
+
+of_find_panel_or_bridge:
 	if (!remote)
 		return -ENODEV;
 
-- 
2.25.1