of/address: Add of_range_count() helper

Some users need a count of the number of ranges entries before
iterating over the entries. Typically this is for allocating some data
structure based on the size. Add a helper, of_range_count(), to get the
count. The helper must be called with an struct of_range_parser
initialized by of_range_parser_init().

Link: https://lore.kernel.org/r/20230328-dt-address-helpers-v1-4-e2456c3e77ab@kernel.orgSigned-off-by: Rob Herring <robh@kernel.org>

drivers/of/unittest.c

@@ -1014,7 +1014,7 @@ static void __init of_unittest_bus_ranges(void)
 	struct of_range range;
 	struct of_range_parser parser;
 	struct resource res;
-	int ret, i = 0;
+	int ret, count, i = 0;
 
 	np = of_find_node_by_path("/testcase-data/address-tests");
 	if (!np) {
@@ -1040,6 +1040,11 @@ static void __init of_unittest_bus_ranges(void)
 		"of_range_to_resource wrong resource start address on node %pOF res=%pR\n",
 		np, &res);
 
+	count = of_range_count(&parser);
+	unittest(count == 2,
+		"of_range_count wrong size on node %pOF count=%d\n",
+		np, count);
+
 	/*
 	 * Get the "ranges" from the device tree
 	 */

include/linux/of_address.h

@@ -35,6 +35,22 @@ struct of_pci_range {
 	for (; of_pci_range_parser_one(parser, range);)
 #define for_each_of_range for_each_of_pci_range
 
+/*
+ * of_range_count - Get the number of "ranges" or "dma-ranges" entries
+ * @parser:	Parser state initialized by of_range_parser_init()
+ *
+ * Returns the number of entries or 0 if none.
+ *
+ * Note that calling this within or after the for_each_of_range() iterator will
+ * be inaccurate giving the number of entries remaining.
+ */
+static inline int of_range_count(const struct of_range_parser *parser)
+{
+	if (!parser || !parser->node || !parser->range || parser->range == parser->end)
+		return 0;
+	return (parser->end - parser->range) / (parser->na + parser->pna + parser->ns);
+}
+
 /* Translate a DMA address from device space to CPU space */
 extern u64 of_translate_dma_address(struct device_node *dev,
 				    const __be32 *in_addr);