mtd: core: set ROOT_DEV for partitions marked as rootfs in DT

This adds support for "linux,rootfs" binding that is used to mark flash
partition containing rootfs. It's useful for devices using device tree
that don't have bootloader passing root info in cmdline.

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20221022211318.32009-2-zajec5@gmail.com

diff --git a/drivers/mtd/mtdcore.c b/drivers/mtd/mtdcore.c
index 756fd27f4cfeef791e8016211d002e256c8865ea..e0193054f8d9fbe16d7bcec77659252646c5dc58 100644 (file)
--- a/drivers/mtd/mtdcore.c
+++ b/drivers/mtd/mtdcore.c
@@ -28,6 +28,7 @@
 #include <linux/leds.h>
 #include <linux/debugfs.h>
 #include <linux/nvmem-provider.h>
+#include <linux/root_dev.h>
 
 #include <linux/mtd/mtd.h>
 #include <linux/mtd/partitions.h>
@@ -737,6 +738,17 @@ int add_mtd_device(struct mtd_info *mtd)
                not->add(mtd);
 
        mutex_unlock(&mtd_table_mutex);
+
+       if (of_find_property(mtd_get_of_node(mtd), "linux,rootfs", NULL)) {
+               if (IS_BUILTIN(CONFIG_MTD)) {
+                       pr_info("mtd: setting mtd%d (%s) as root device\n", mtd->index, mtd->name);
+                       ROOT_DEV = MKDEV(MTD_BLOCK_MAJOR, mtd->index);
+               } else {
+                       pr_warn("mtd: can't set mtd%d (%s) as root device - mtd must be builtin\n",
+                               mtd->index, mtd->name);
+               }
+       }
+
        /* We _know_ we aren't being removed, because
           our caller is still holding us here. So none
           of this try_ nonsense, and no bitching about it