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Subject[PATCH v2 1/9] of: add helper to lookup compatible child node
Date
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>
---
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 466e3c8582f0..bc420d2aa5f5 100644
--- 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 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)
--
2.18.0
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