of: Add new helper of_parse_phandles_with_args()

The helper is factored out of of_get_gpio(). Will be used by the QE
pin multiplexing functions (they need to parse the gpios = <> too).

Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

drivers/of/base.c

@@ -458,3 +458,112 @@ int of_modalias_node(struct device_node *node, char *modalias, int len)
 }
 EXPORT_SYMBOL_GPL(of_modalias_node);
 
+/**
+ * of_parse_phandles_with_args - Find a node pointed by phandle in a list
+ * @np:		pointer to a device tree node containing a list
+ * @list_name:	property name that contains a list
+ * @cells_name:	property name that specifies phandles' arguments count
+ * @index:	index of a phandle to parse out
+ * @out_node:	pointer to device_node struct pointer (will be filled)
+ * @out_args:	pointer to arguments pointer (will be filled)
+ *
+ * This function is useful to parse lists of phandles and their arguments.
+ * Returns 0 on success and fills out_node and out_args, on error returns
+ * appropriate errno value.
+ *
+ * Example:
+ *
+ * phandle1: node1 {
+ * 	#list-cells = <2>;
+ * }
+ *
+ * phandle2: node2 {
+ * 	#list-cells = <1>;
+ * }
+ *
+ * node3 {
+ * 	list = <&phandle1 1 2 &phandle2 3>;
+ * }
+ *
+ * To get a device_node of the `node2' node you may call this:
+ * of_parse_phandles_with_args(node3, "list", "#list-cells", 2, &node2, &args);
+ */
+int of_parse_phandles_with_args(struct device_node *np, const char *list_name,
+				const char *cells_name, int index,
+				struct device_node **out_node,
+				const void **out_args)
+{
+	int ret = -EINVAL;
+	const u32 *list;
+	const u32 *list_end;
+	int size;
+	int cur_index = 0;
+	struct device_node *node = NULL;
+	const void *args;
+
+	list = of_get_property(np, list_name, &size);
+	if (!list) {
+		ret = -ENOENT;
+		goto err0;
+	}
+	list_end = list + size / sizeof(*list);
+
+	while (list < list_end) {
+		const u32 *cells;
+		const phandle *phandle;
+
+		phandle = list;
+		args = list + 1;
+
+		/* one cell hole in the list = <>; */
+		if (!*phandle) {
+			list++;
+			goto next;
+		}
+
+		node = of_find_node_by_phandle(*phandle);
+		if (!node) {
+			pr_debug("%s: could not find phandle\n",
+				 np->full_name);
+			goto err0;
+		}
+
+		cells = of_get_property(node, cells_name, &size);
+		if (!cells || size != sizeof(*cells)) {
+			pr_debug("%s: could not get %s for %s\n",
+				 np->full_name, cells_name, node->full_name);
+			goto err1;
+		}
+
+		/* Next phandle is at offset of one phandle cell + #cells */
+		list += 1 + *cells;
+		if (list > list_end) {
+			pr_debug("%s: insufficient arguments length\n",
+				 np->full_name);
+			goto err1;
+		}
+next:
+		if (cur_index == index)
+			break;
+
+		of_node_put(node);
+		node = NULL;
+		cur_index++;
+	}
+
+	if (!node) {
+		ret = -ENOENT;
+		goto err0;
+	}
+
+	*out_node = node;
+	*out_args = args;
+
+	return 0;
+err1:
+	of_node_put(node);
+err0:
+	pr_debug("%s failed with status %d\n", __func__, ret);
+	return ret;
+}
+EXPORT_SYMBOL(of_parse_phandles_with_args);