of: search the best compatible match first in __of_match_node()

Currently, of_match_node compares each given match against all node's
compatible strings with of_device_is_compatible.

To achieve multiple compatible strings per node with ordering from
specific to generic, this requires given matches to be ordered from
specific to generic. For most of the drivers this is not true and also
an alphabetical ordering is more sane there.

Therefore, this patch introduces a function to match each of the node's
compatible strings against all given compatible matches without type and
name first, before checking the next compatible string. This implies
that node's compatibles are ordered from specific to generic while
given matches can be in any order. If we fail to find such a match
entry, then fall-back to the old method in order to keep compatibility.

Cc: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
Signed-off-by: Kevin Hao <haokexin@gmail.com>
Tested-by: Stephen Chivers <schivers@csc.com>
Signed-off-by: Rob Herring <robh@kernel.org>

drivers/of/base.c

@@ -730,13 +730,49 @@ out:
 }
 EXPORT_SYMBOL(of_find_node_with_property);
 
+static const struct of_device_id *
+of_match_compatible(const struct of_device_id *matches,
+			const struct device_node *node)
+{
+	const char *cp;
+	int cplen, l;
+	const struct of_device_id *m;
+
+	cp = __of_get_property(node, "compatible", &cplen);
+	while (cp && (cplen > 0)) {
+		m = matches;
+		while (m->name[0] || m->type[0] || m->compatible[0]) {
+			/* Only match for the entries without type and name */
+			if (m->name[0] || m->type[0] ||
+				of_compat_cmp(m->compatible, cp,
+					 strlen(m->compatible)))
+				m++;
+			else
+				return m;
+		}
+
+		/* Get node's next compatible string */
+		l = strlen(cp) + 1;
+		cp += l;
+		cplen -= l;
+	}
+
+	return NULL;
+}
+
 static
 const struct of_device_id *__of_match_node(const struct of_device_id *matches,
 					   const struct device_node *node)
 {
+	const struct of_device_id *m;
+
 	if (!matches)
 		return NULL;
 
+	m = of_match_compatible(matches, node);
+	if (m)
+		return m;
+
 	while (matches->name[0] || matches->type[0] || matches->compatible[0]) {
 		int match = 1;
 		if (matches->name[0])
@@ -760,7 +796,12 @@ const struct of_device_id *__of_match_node(const struct of_device_id *matches,
  *	@matches:	array of of device match structures to search in
  *	@node:		the of device structure to match against
  *
- *	Low level utility function used by device matching.
+ *	Low level utility function used by device matching. We have two ways
+ *	of matching:
+ *	- Try to find the best compatible match by comparing each compatible
+ *	  string of device node with all the given matches respectively.
+ *	- If the above method failed, then try to match the compatible by using
+ *	  __of_device_is_compatible() besides the match in type and name.
  */
 const struct of_device_id *of_match_node(const struct of_device_id *matches,
 					 const struct device_node *node)