[PATCH v3] drm: of: Lookup if child node has panel or bridge

[Jagan Teki <jagan@amarulasolutions.com>]

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.

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>;
        };
};

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.
+	 *
+	 * Lookup that child node for a given parent however that child is
+	 * neither a 'port' nor a 'ports' node.
+	 */
+	for_each_available_child_of_node(np, remote) {
+		if (of_node_name_eq(remote, "port") ||
+		    of_node_name_eq(remote, "ports"))
+			continue;
+
+		goto of_find_panel_or_bridge;
+	}
+
 	/*
 	 * 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 +275,8 @@ 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