of: add helper for getting endpoint node of specific identifiers

When there are multiple ports or multiple endpoints in a port, they have to be
distinguished by the value of reg property. It is common. The drivers can get
the specific endpoint in the specific port via this function. Now the drivers
have to implement this code in themselves or have to force the order of dt nodes
to get the right node.

Signed-off-by: Hyungwon Hwang <human.hwang@samsung.com>
Acked-by: Rob Herring <robh+dt@kernel.org>
Signed-off-by: Inki Dae <inki.dae@samsung.com>

drivers/of/base.c

@@ -2232,6 +2232,39 @@ struct device_node *of_graph_get_next_endpoint(const struct device_node *parent,
 }
 EXPORT_SYMBOL(of_graph_get_next_endpoint);
 
+/**
+ * of_graph_get_endpoint_by_regs() - get endpoint node of specific identifiers
+ * @parent: pointer to the parent device node
+ * @port_reg: identifier (value of reg property) of the parent port node
+ * @reg: identifier (value of reg property) of the endpoint node
+ *
+ * Return: An 'endpoint' node pointer which is identified by reg and at the same
+ * is the child of a port node identified by port_reg. reg and port_reg are
+ * ignored when they are -1.
+ */
+struct device_node *of_graph_get_endpoint_by_regs(
+	const struct device_node *parent, int port_reg, int reg)
+{
+	struct of_endpoint endpoint;
+	struct device_node *node, *prev_node = NULL;
+
+	while (1) {
+		node = of_graph_get_next_endpoint(parent, prev_node);
+		of_node_put(prev_node);
+		if (!node)
+			break;
+
+		of_graph_parse_endpoint(node, &endpoint);
+		if (((port_reg == -1) || (endpoint.port == port_reg)) &&
+			((reg == -1) || (endpoint.id == reg)))
+			return node;
+
+		prev_node = node;
+	}
+
+	return NULL;
+}
+
 /**
  * of_graph_get_remote_port_parent() - get remote port's parent node
  * @node: pointer to a local endpoint device_node

include/linux/of_graph.h

@@ -45,6 +45,8 @@ int of_graph_parse_endpoint(const struct device_node *node,
 struct device_node *of_graph_get_port_by_id(struct device_node *node, u32 id);
 struct device_node *of_graph_get_next_endpoint(const struct device_node *parent,
 					struct device_node *previous);
+struct device_node *of_graph_get_endpoint_by_regs(
+		const struct device_node *parent, int port_reg, int reg);
 struct device_node *of_graph_get_remote_port_parent(
 					const struct device_node *node);
 struct device_node *of_graph_get_remote_port(const struct device_node *node);
@@ -69,6 +71,12 @@ static inline struct device_node *of_graph_get_next_endpoint(
 	return NULL;
 }
 
+struct device_node *of_graph_get_endpoint_by_regs(
+		const struct device_node *parent, int port_reg, int reg)
+{
+	return NULL;
+}
+
 static inline struct device_node *of_graph_get_remote_port_parent(
 					const struct device_node *node)
 {