linux-kernel - [PATCH V3 2/2] mtd: core: set ROOT_DEV for partitions marked as rootfs in DT

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Date:   Sat, 22 Oct 2022 23:13:18 +0200
From:   Rafał Miłecki <zajec5@...il.com>
To:     Miquel Raynal <miquel.raynal@...tlin.com>,
        Richard Weinberger <richard@....at>,
        Vignesh Raghavendra <vigneshr@...com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>
Cc:     Mikhail Zhilkin <csharper2005@...il.com>,
        Christian Marangi <ansuelsmth@...il.com>,
        Wolfram Sang <wsa+renesas@...g-engineering.com>,
        Chaitanya Kulkarni <kch@...dia.com>,
        "Martin K . Petersen" <martin.petersen@...cle.com>,
        Jens Axboe <axboe@...nel.dk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-mtd@...ts.infradead.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Rafał Miłecki <rafal@...ecki.pl>
Subject: [PATCH V3 2/2] mtd: core: set ROOT_DEV for partitions marked as rootfs in DT

From: Rafał Miłecki <rafal@...ecki.pl>

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@...ecki.pl>
---
V2: Use "linux,rootfs" as more accurate. Thanks Rob.
V3: Add IS_BUILTIN(CONFIG_MTD) check to avoid
    ERROR: modpost: "ROOT_DEV" [drivers/mtd/mtd.ko] undefined!
---
 drivers/mtd/mtdcore.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/drivers/mtd/mtdcore.c b/drivers/mtd/mtdcore.c
index 20fcedc3021e..f70a5e66843b 100644
--- 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>
@@ -735,6 +736,17 @@ 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
-- 
2.34.1