of: base: Add for_each_child_of_node_with_prefix()

There are cases where drivers would go through child device nodes and
operate on only the ones whose node name starts with a given prefix.

Provide a helper for these users. This will mainly be used in a
subsequent patch that implements a hardware component prober for I2C
busses.

Signed-off-by: Chen-Yu Tsai <wenst@chromium.org>
Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>

drivers/of/base.c

@@ -644,6 +644,41 @@ struct device_node *of_get_next_child(const struct device_node *node,
 }
 EXPORT_SYMBOL(of_get_next_child);
 
+/**
+ * of_get_next_child_with_prefix - Find the next child node with prefix
+ * @node:	parent node
+ * @prev:	previous child of the parent node, or NULL to get first
+ *
+ * This function is like of_get_next_child(), except that it automatically
+ * skips any nodes whose name doesn't have the given prefix.
+ *
+ * Return: A node pointer with refcount incremented, use
+ * of_node_put() on it when done.
+ */
+struct device_node *of_get_next_child_with_prefix(const struct device_node *node,
+						  struct device_node *prev,
+						  const char *prefix)
+{
+	struct device_node *next;
+	unsigned long flags;
+
+	if (!node)
+		return NULL;
+
+	raw_spin_lock_irqsave(&devtree_lock, flags);
+	next = prev ? prev->sibling : node->child;
+	for (; next; next = next->sibling) {
+		if (!of_node_name_prefix(next, prefix))
+			continue;
+		if (of_node_get(next))
+			break;
+	}
+	of_node_put(prev);
+	raw_spin_unlock_irqrestore(&devtree_lock, flags);
+	return next;
+}
+EXPORT_SYMBOL(of_get_next_child_with_prefix);
+
 static struct device_node *of_get_next_status_child(const struct device_node *node,
 						    struct device_node *prev,
 						    bool (*checker)(const struct device_node *))

include/linux/of.h

@@ -289,6 +289,9 @@ extern struct device_node *of_get_parent(const struct device_node *node);
 extern struct device_node *of_get_next_parent(struct device_node *node);
 extern struct device_node *of_get_next_child(const struct device_node *node,
 					     struct device_node *prev);
+extern struct device_node *of_get_next_child_with_prefix(const struct device_node *node,
+							 struct device_node *prev,
+							 const char *prefix);
 extern struct device_node *of_get_next_available_child(
 	const struct device_node *node, struct device_node *prev);
 extern struct device_node *of_get_next_reserved_child(
@@ -1468,6 +1471,12 @@ static inline int of_property_read_s32(const struct device_node *np,
 	     child != NULL;						\
 	     child = of_get_next_child(parent, child))
 
+#define for_each_child_of_node_with_prefix(parent, child, prefix)	\
+	for (struct device_node *child __free(device_node) =		\
+	     of_get_next_child_with_prefix(parent, NULL, prefix);	\
+	     child != NULL;						\
+	     child = of_get_next_child_with_prefix(parent, child, prefix))
+
 #define for_each_available_child_of_node(parent, child) \
 	for (child = of_get_next_available_child(parent, NULL); child != NULL; \
 	     child = of_get_next_available_child(parent, child))