of: add helper to lookup compatible child node

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>

1 files changed, 8 insertions, 0 deletions

diff --git a/include/linux/of.h b/include/linux/of.h
index 4d25e4f952d9..b99a1a8c2952 100644
--- a/include/linux/of.h
+++ b/include/linux/of.h
@@ -290,6 +290,8 @@ 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);
 
@@ -632,6 +634,12 @@ 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)