[PATCH V8 1/2] mtd: partitions: add of_match_table parser matching

[Rafał Miłecki]

From: Brian Norris <computersforpeace at gmail.com>

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

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.

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 at gmail.com>
Signed-off-by: Rafał Miłecki <rafal at milecki.pl>
---
This is based on Brian's patches:
[RFC PATCH 4/7] mtd: add of_match_mtd_parser() and of_mtd_match_mtd_parser() helpers
[RFC PATCH 6/7] RFC: mtd: partitions: enable of_match_table matching

V1: Put helpers in mtdpart.c instead of drivers/of/of_mtd.c
    Merge helpers into a single of_mtd_match_mtd_parser
V3: Add a simple comment to note we will need the best match in the future
V4: Rework new functions to pick parser with the best match
    Move new code in parse_mtd_partitions up so it has precedence over flash
    driver defaults and MTD defaults
V5: Rework matching code to start checking with the most specific string in the
    "compatibility" property.
V6: Initialize "ret" variable in mtd_part_get_parser_by_cp to NULL
V7: Rename function "mtd_part_get_parser_by_cp" to use "_compatible_"
    Rename "cp" variable to "compat"
    Drop unneeded if (np) check from the parse_mtd_partitions
V8: Move new OF code in parse_mtd_partitions() lower so driver-specified parsers
    take a precedence. Update commit message to make that clear.
---
 drivers/mtd/mtdpart.c          | 60 ++++++++++++++++++++++++++++++++++++++++++
 include/linux/mtd/partitions.h |  1 +
 2 files changed, 61 insertions(+)

diff --git a/drivers/mtd/mtdpart.c b/drivers/mtd/mtdpart.c
index 76cd21d1171b..e33bad0e46f5 100644
--- a/drivers/mtd/mtdpart.c
+++ b/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"
 
@@ -861,6 +862,45 @@ static int mtd_part_do_parse(struct mtd_part_parser *parser,
 }
 
 /**
+ * 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;
+}
+
+/**
  * parse_mtd_partitions - parse MTD partitions
  * @master: the master partition (describes whole MTD device)
  * @types: names of partition parsers to try or %NULL
@@ -886,6 +926,9 @@ int parse_mtd_partitions(struct mtd_info *master, const char *const *types,
 			 struct mtd_part_parser_data *data)
 {
 	struct mtd_part_parser *parser;
+	struct device_node *np;
+	struct property *prop;
+	const char *compat;
 	int ret, err = 0;
 
 	if (!types)
@@ -912,6 +955,23 @@ int parse_mtd_partitions(struct mtd_info *master, const char *const *types,
 		if (ret < 0 && !err)
 			err = ret;
 	}
+
+	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, data);
+		if (ret > 0) {
+			of_node_put(np);
+			return 0;
+		}
+		mtd_part_parser_put(parser);
+		if (ret < 0 && !err)
+			err = ret;
+	}
+	of_node_put(np);
+
 	return err;
 }
 
diff --git a/include/linux/mtd/partitions.h b/include/linux/mtd/partitions.h
index c4beb70dacbd..11cb0c50cd84 100644
--- a/include/linux/mtd/partitions.h
+++ b/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);
-- 
2.11.0