libfdt: Add a subnodes iterator macro

The fdt_for_each_subnode() iterator macro provided by this patch can be
used to iterate over a device tree node's subnodes. At each iteration a
loop variable will be set to the next subnode.

Signed-off-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

libfdt/libfdt.h

@@ -168,6 +168,34 @@ int fdt_first_subnode(const void *fdt, int offset);
  */
 int fdt_next_subnode(const void *fdt, int offset);
 
+/**
+ * fdt_for_each_subnode - iterate over all subnodes of a parent
+ *
+ * @node:	child node (int, lvalue)
+ * @fdt:	FDT blob (const void *)
+ * @parent:	parent node (int)
+ *
+ * This is actually a wrapper around a for loop and would be used like so:
+ *
+ *	fdt_for_each_subnode(node, fdt, parent) {
+ *		Use node
+ *		...
+ *	}
+ *
+ *	if ((node < 0) && (node != -FDT_ERR_NOT_FOUND)) {
+ *		Error handling
+ *	}
+ *
+ * Note that this is implemented as a macro and @node is used as
+ * iterator in the loop. The parent variable be constant or even a
+ * literal.
+ *
+ */
+#define fdt_for_each_subnode(node, fdt, parent)		\
+	for (node = fdt_first_subnode(fdt, parent);	\
+	     node >= 0;					\
+	     node = fdt_next_subnode(fdt, node))
+
 /**********************************************************************/
 /* General functions                                                  */
 /**********************************************************************/

tests/subnode_iterate.c

@@ -48,9 +48,7 @@ static void test_node(void *fdt, int parent_offset)
 	subnodes = cpu_to_fdt32(*prop);
 
 	count = 0;
-	for (offset = fdt_first_subnode(fdt, parent_offset);
+	fdt_for_each_subnode(offset, fdt, parent_offset)
-	     offset >= 0;
-	     offset = fdt_next_subnode(fdt, offset))
 		count++;
 
 	if (count != subnodes) {
@@ -65,9 +63,7 @@ static void check_fdt_next_subnode(void *fdt)
 	int offset;
 	int count = 0;
 
-	for (offset = fdt_first_subnode(fdt, 0);
+	fdt_for_each_subnode(offset, fdt, 0) {
-	     offset >= 0;
-	     offset = fdt_next_subnode(fdt, offset)) {
 		test_node(fdt, offset);
 		count++;
 	}