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>

diff --git a/drivers/of/base.c b/drivers/of/base.c
index 466e3c8582f0fd62628b90872b2046971e064776..bc420d2aa5f5726075416753683f9f8cefed7d76 100644 (file)
--- a/drivers/of/base.c
+++ b/drivers/of/base.c
@@ -719,6 +719,31 @@ 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 4d25e4f952d9bd4c02b1f3c33fea0c4254907e14..b99a1a8c295211d33979dfb06dea78b96296b53b 100644 (file)
--- 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)