[PATCH 4.4 25/86] of: add helper to lookup compatible child node

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

[ Upstream commit 36156f9241cb0f9e37d998052873ca7501ad4b36 ]

Add of_get_compatible_child() helper that can be used to lookup
compatible child nodes.

Several drivers currently use of_find_compatible_node() to lookup child
nodes while failing to notice that the of_find_ functions search the
entire tree depth-first (from a given start node) and therefore can
match unrelated nodes. The fact that these functions also drop a
reference to the node they start searching from (e.g. the parent node)
is typically also overlooked, something which can lead to use-after-free
bugs.

Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Rob Herring <robh@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/of/base.c  | 25 +++++++++++++++++++++++++
 include/linux/of.h |  8 ++++++++
 2 files changed, 33 insertions(+)

diff --git a/drivers/of/base.c b/drivers/of/base.c
index 31341290cd91..c6e019208d17 100644
--- a/drivers/of/base.c
+++ b/drivers/of/base.c
@@ -712,6 +712,31 @@ struct device_node *of_get_next_available_child(const struct device_node *node,
 }
 EXPORT_SYMBOL(of_get_next_available_child);
 
+/**
+ * of_get_compatible_child - Find compatible child node
+ * @parent:	parent node
+ * @compatible:	compatible string
+ *
+ * Lookup child node whose compatible property contains the given compatible
+ * string.
+ *
+ * Returns a node pointer with refcount incremented, use of_node_put() on it
+ * when done; or NULL if not found.
+ */
+struct device_node *of_get_compatible_child(const struct device_node *parent,
+				const char *compatible)
+{
+	struct device_node *child;
+
+	for_each_child_of_node(parent, child) {
+		if (of_device_is_compatible(child, compatible))
+			break;
+	}
+
+	return child;
+}
+EXPORT_SYMBOL(of_get_compatible_child);
+
 /**
  *	of_get_child_by_name - Find the child node by name for a given parent
  *	@node:	parent node
diff --git a/include/linux/of.h b/include/linux/of.h
index dd10626a615f..d9371c9cd88a 100644
--- a/include/linux/of.h
+++ b/include/linux/of.h
@@ -265,6 +265,8 @@ extern struct device_node *of_get_next_child(const struct device_node *node,
 extern struct device_node *of_get_next_available_child(
 	const struct device_node *node, struct device_node *prev);
 
+extern struct device_node *of_get_compatible_child(const struct device_node *parent,
+					const char *compatible);
 extern struct device_node *of_get_child_by_name(const struct device_node *node,
 					const char *name);
 
@@ -462,6 +464,12 @@ static inline bool of_have_populated_dt(void)
 	return false;
 }
 
+static inline struct device_node *of_get_compatible_child(const struct device_node *parent,
+					const char *compatible)
+{
+	return NULL;
+}
+
 static inline struct device_node *of_get_child_by_name(
 					const struct device_node *node,
 					const char *name)
-- 
2.17.1