[PATCH v9 1/2] of_graph: add of_graph_is_present()

[Dmitry Osipenko <digetx@gmail.com>]

In some case, like a DRM display code for example, it's useful to silently
check whether port node exists at all in a device-tree before proceeding
with parsing of the graph.

This patch adds of_graph_is_present() which returns true if given
device-tree node contains OF graph port.

Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
---
 drivers/of/property.c    | 52 +++++++++++++++++++++++++++++++++-------
 include/linux/of_graph.h |  6 +++++
 2 files changed, 49 insertions(+), 9 deletions(-)

diff --git a/drivers/of/property.c b/drivers/of/property.c
index 6a5760f0d6cd..e12b8b491837 100644
--- a/drivers/of/property.c
+++ b/drivers/of/property.c
@@ -29,6 +29,48 @@
 
 #include "of_private.h"
 
+/**
+ * of_graph_get_first_local_port() - get first local port node
+ * @node: pointer to a local endpoint device_node
+ *
+ * Return: First local port node associated with local endpoint node linked
+ *	   to @node. Use of_node_put() on it when done.
+ */
+static struct device_node *
+of_graph_get_first_local_port(const struct device_node *node)
+{
+	struct device_node *ports, *port;
+
+	ports = of_get_child_by_name(node, "ports");
+	if (ports)
+		node = ports;
+
+	port = of_get_child_by_name(node, "port");
+	of_node_put(ports);
+
+	return port;
+}
+
+/**
+ * of_graph_is_present() - check graph's presence
+ * @node: pointer to a device_node checked for the graph's presence
+ *
+ * Return: True if @node has a port or ports sub-node, false otherwise.
+ */
+bool of_graph_is_present(const struct device_node *node)
+{
+	struct device_node *local;
+
+	local = of_graph_get_first_local_port(node);
+	if (!local)
+		return false;
+
+	of_node_put(local);
+
+	return true;
+}
+EXPORT_SYMBOL(of_graph_is_present);
+
 /**
  * of_property_count_elems_of_size - Count the number of elements in a property
  *
@@ -608,15 +650,7 @@ struct device_node *of_graph_get_next_endpoint(const struct device_node *parent,
 	 * parent port node.
 	 */
 	if (!prev) {
-		struct device_node *node;
-
-		node = of_get_child_by_name(parent, "ports");
-		if (node)
-			parent = node;
-
-		port = of_get_child_by_name(parent, "port");
-		of_node_put(node);
-
+		port = of_graph_get_first_local_port(parent);
 		if (!port) {
 			pr_err("graph: no port node found in %pOF\n", parent);
 			return NULL;
diff --git a/include/linux/of_graph.h b/include/linux/of_graph.h
index 01038a6aade0..4d7756087b6b 100644
--- a/include/linux/of_graph.h
+++ b/include/linux/of_graph.h
@@ -38,6 +38,7 @@ struct of_endpoint {
 	     child = of_graph_get_next_endpoint(parent, child))
 
 #ifdef CONFIG_OF
+bool of_graph_is_present(const struct device_node *node);
 int of_graph_parse_endpoint(const struct device_node *node,
 				struct of_endpoint *endpoint);
 int of_graph_get_endpoint_count(const struct device_node *np);
@@ -56,6 +57,11 @@ struct device_node *of_graph_get_remote_node(const struct device_node *node,
 					     u32 port, u32 endpoint);
 #else
 
+static inline bool of_graph_is_present(const struct device_node *node)
+{
+	return false;
+}
+
 static inline int of_graph_parse_endpoint(const struct device_node *node,
 					struct of_endpoint *endpoint)
 {
-- 
2.26.0