[POWERPC] Add of_get_next_parent()

Iterating through a device node's parents is simple enough, but dealing
with the refcounts properly is a little ugly, and replicating that logic
is asking for someone to get it wrong or forget it all together, eg:

while (dn != NULL) {
	/* loop body */
	tmp = of_get_parent(dn);
	of_node_put(dn);
	dn = tmp;
}

So add of_get_next_parent(), inspired by of_get_next_child().  The
contract is that it returns the parent and drops the reference on the
current node, this makes the loop look like:

while (dn != NULL) {
	/* loop body */
	dn = of_get_next_parent(dn);
}

Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Acked-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Paul Mackerras <paulus@samba.org>

2 files changed, 26 insertions, 0 deletions

diff --git a/drivers/of/base.c b/drivers/of/base.c
index b306fef1ac41..80c9deca5f35 100644
--- a/drivers/of/base.c
+++ b/drivers/of/base.c
@@ -138,6 +138,31 @@ struct device_node *of_get_parent(const struct device_node *node)
 EXPORT_SYMBOL(of_get_parent);
 
 /**
+ *      of_get_next_parent - Iterate to a node's parent
+ *      @node:  Node to get parent of
+ *
+ *      This is like of_get_parent() except that it drops the
+ *      refcount on the passed node, making it suitable for iterating
+ *      through a node's parents.
+ *
+ *      Returns a node pointer with refcount incremented, use
+ *      of_node_put() on it when done.
+ */
+struct device_node *of_get_next_parent(struct device_node *node)
+{
+        struct device_node *parent;
+
+        if (!node)
+                return NULL;
+
+        read_lock(&devtree_lock);
+        parent = of_node_get(node->parent);
+        of_node_put(node);
+        read_unlock(&devtree_lock);
+        return parent;
+}
+
+/**
  *      of_get_next_child - Iterate a node childs
  *      @node:  parent node
  *      @prev:  previous child of the parent node, or NULL to get first
diff --git a/include/linux/of.h b/include/linux/of.h
index b5f33efcb8e2..6981016dcc25 100644
--- a/include/linux/of.h
+++ b/include/linux/of.h
@@ -50,6 +50,7 @@ extern struct device_node *of_find_matching_node(struct device_node *from,
 extern struct device_node *of_find_node_by_path(const char *path);
 extern struct device_node *of_find_node_by_phandle(phandle handle);
 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);
 #define for_each_child_of_node(parent, child) \