mtd: partitions: add of_match_table parser matching for the "ofpart" type

In order to properly support compatibility strings as described in the
bindings/mtd/partition.txt "ofpart" type should be treated as an
indication for looking into OF. MTD should check "compatible" property
and search for a matching parser rather than blindly trying the one
supporting "fixed-partitions".

It also means that existing "fixed-partitions" parser should get renamed
to use a more meaningful name.

This commit achievies that aim by introducing a new mtd_part_of_parse().
It works by looking for a matching parser for every string in the
"compatibility" property (starting with the most specific one).

Please note that driver-specified parsers still take a precedence. It's
assumed that driver providing a parser type has a good reason for that
(e.g. having platform data with device-specific info). Also doing
otherwise could break existing setups. The same applies to using default
parsers (including "cmdlinepart") as some overwrite DT data with cmdline
argument.

Partition parsers can now provide an of_match_table to enable
flash<-->parser matching via device tree as documented in the
mtd/partition.txt.

This support is currently limited to built-in parsers as it uses
request_module() and friends. This should be sufficient for most cases
though as compiling parsers as modules isn't a common choice.

Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Tested-by: Peter Rosin <peda@axentia.se>
Reviewed-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>

drivers/mtd/mtdpart.c

@@ -30,6 +30,7 @@
 #include <linux/mtd/mtd.h>
 #include <linux/mtd/partitions.h>
 #include <linux/err.h>
+#include <linux/of.h>
 
 #include "mtdcore.h"
 
@@ -845,6 +846,92 @@ static int mtd_part_do_parse(struct mtd_part_parser *parser,
 	return ret;
 }
 
+/**
+ * mtd_part_get_compatible_parser - find MTD parser by a compatible string
+ *
+ * @compat: compatible string describing partitions in a device tree
+ *
+ * MTD parsers can specify supported partitions by providing a table of
+ * compatibility strings. This function finds a parser that advertises support
+ * for a passed value of "compatible".
+ */
+static struct mtd_part_parser *mtd_part_get_compatible_parser(const char *compat)
+{
+	struct mtd_part_parser *p, *ret = NULL;
+
+	spin_lock(&part_parser_lock);
+
+	list_for_each_entry(p, &part_parsers, list) {
+		const struct of_device_id *matches;
+
+		matches = p->of_match_table;
+		if (!matches)
+			continue;
+
+		for (; matches->compatible[0]; matches++) {
+			if (!strcmp(matches->compatible, compat) &&
+			    try_module_get(p->owner)) {
+				ret = p;
+				break;
+			}
+		}
+
+		if (ret)
+			break;
+	}
+
+	spin_unlock(&part_parser_lock);
+
+	return ret;
+}
+
+static int mtd_part_of_parse(struct mtd_info *master,
+			     struct mtd_partitions *pparts)
+{
+	struct mtd_part_parser *parser;
+	struct device_node *np;
+	struct property *prop;
+	const char *compat;
+	const char *fixed = "ofpart";
+	int ret, err = 0;
+
+	np = of_get_child_by_name(mtd_get_of_node(master), "partitions");
+	of_property_for_each_string(np, "compatible", prop, compat) {
+		parser = mtd_part_get_compatible_parser(compat);
+		if (!parser)
+			continue;
+		ret = mtd_part_do_parse(parser, master, pparts, NULL);
+		if (ret > 0) {
+			of_node_put(np);
+			return ret;
+		}
+		mtd_part_parser_put(parser);
+		if (ret < 0 && !err)
+			err = ret;
+	}
+	of_node_put(np);
+
+	/*
+	 * For backward compatibility we have to try the "ofpart"
+	 * parser. It supports old DT format with partitions specified as a
+	 * direct subnodes of a flash device DT node without any compatibility
+	 * specified we could match.
+	 */
+	parser = mtd_part_parser_get(fixed);
+	if (!parser && !request_module("%s", fixed))
+		parser = mtd_part_parser_get(fixed);
+	if (parser) {
+		ret = mtd_part_do_parse(parser, master, pparts, NULL);
+		if (ret > 0)
+			return ret;
+		mtd_part_parser_put(parser);
+		if (ret < 0 && !err)
+			err = ret;
+	}
+
+	return err;
+}
+
 /**
  * parse_mtd_partitions - parse MTD partitions
  * @master: the master partition (describes whole MTD device)
@@ -877,19 +964,30 @@ int parse_mtd_partitions(struct mtd_info *master, const char *const *types,
 		types = default_mtd_part_types;
 
 	for ( ; *types; types++) {
-		pr_debug("%s: parsing partitions %s\n", master->name, *types);
-		parser = mtd_part_parser_get(*types);
-		if (!parser && !request_module("%s", *types))
+		/*
+		 * ofpart is a special type that means OF partitioning info
+		 * should be used. It requires a bit different logic so it is
+		 * handled in a separated function.
+		 */
+		if (!strcmp(*types, "ofpart")) {
+			ret = mtd_part_of_parse(master, pparts);
+		} else {
+			pr_debug("%s: parsing partitions %s\n", master->name,
+				 *types);
 			parser = mtd_part_parser_get(*types);
-		pr_debug("%s: got parser %s\n", master->name,
-			 parser ? parser->name : NULL);
-		if (!parser)
-			continue;
-		ret = mtd_part_do_parse(parser, master, pparts, data);
+			if (!parser && !request_module("%s", *types))
+				parser = mtd_part_parser_get(*types);
+			pr_debug("%s: got parser %s\n", master->name,
+				parser ? parser->name : NULL);
+			if (!parser)
+				continue;
+			ret = mtd_part_do_parse(parser, master, pparts, data);
+			if (ret <= 0)
+				mtd_part_parser_put(parser);
+		}
 		/* Found partitions! */
 		if (ret > 0)
 			return 0;
-		mtd_part_parser_put(parser);
 		/*
 		 * Stash the first error we see; only report it if no parser
 		 * succeeds

include/linux/mtd/partitions.h

@@ -77,6 +77,7 @@ struct mtd_part_parser {
 	struct list_head list;
 	struct module *owner;
 	const char *name;
+	const struct of_device_id *of_match_table;
 	int (*parse_fn)(struct mtd_info *, const struct mtd_partition **,
 			struct mtd_part_parser_data *);
 	void (*cleanup)(const struct mtd_partition *pparts, int nr_parts);