mtd: call of_platform_populate() for MTD partitions

Until this change MTD subsystem supported handling partitions only with
MTD partitions parsers. That's a specific / limited API designed around
partitions.

Some MTD partitions may however require different handling. They may
contain specific data that needs to be parsed and somehow extracted. For
that purpose MTD subsystem should allow binding of standard platform
drivers.

An example can be U-Boot (sub)partition with environment variables.
There exist a "u-boot,env" DT binding for MTD (sub)partition that
requires an NVMEM driver.

Ref: 5db1c2dbc0 ("dt-bindings: nvmem: add U-Boot environment variables binding")
Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20220510131259.555-1-zajec5@gmail.com

drivers/mtd/mtdpart.c

@@ -17,6 +17,7 @@
 #include <linux/mtd/partitions.h>
 #include <linux/err.h>
 #include <linux/of.h>
+#include <linux/of_platform.h>
 
 #include "mtdcore.h"
 
@@ -577,10 +578,16 @@ static int mtd_part_of_parse(struct mtd_info *master,
 	struct mtd_part_parser *parser;
 	struct device_node *np;
 	struct property *prop;
+	struct device *dev;
 	const char *compat;
 	const char *fixed = "fixed-partitions";
 	int ret, err = 0;
 
+	dev = &master->dev;
+	/* Use parent device (controller) if the top level MTD is not registered */
+	if (!IS_ENABLED(CONFIG_MTD_PARTITIONED_MASTER) && !mtd_is_partition(master))
+		dev = master->dev.parent;
+
 	np = mtd_get_of_node(master);
 	if (mtd_is_partition(master))
 		of_node_get(np);
@@ -593,6 +600,7 @@ static int mtd_part_of_parse(struct mtd_info *master,
 			continue;
 		ret = mtd_part_do_parse(parser, master, pparts, NULL);
 		if (ret > 0) {
+			of_platform_populate(np, NULL, NULL, dev);
 			of_node_put(np);
 			return ret;
 		}
@@ -600,6 +608,7 @@ static int mtd_part_of_parse(struct mtd_info *master,
 		if (ret < 0 && !err)
 			err = ret;
 	}
+	of_platform_populate(np, NULL, NULL, dev);
 	of_node_put(np);
 
 	/*