[PATCH v2 4/4] mtd: nand: mxc_nand: Only automatically create BBT if NAND seems to be pristine

["Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>]

Automatically creating a BBT is the right thing to do if the NAND is
factory new. However when migrating from a barebox older than commit
v2020.03.0~28^2~1 ("mtd: nand-imx: Create BBT automatically when
necessary") on a used machine, this automatism is really bad because it
most likely marks the blocks containing the barebox image (and possibly
more) as bad. On such a system the vendor BBMs are gone, but it was
operated without that information before, so continuing to do so is a
sane option.

Add a light check for the NAND to be really pristine: If any block looks
like containing a barebox image or a UBI refuse to create a BBT.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
---
 drivers/mtd/nand/raw/mxc_nand.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/drivers/mtd/nand/raw/mxc_nand.c b/drivers/mtd/nand/raw/mxc_nand.c
index faea1c95f95e..f8517df823e5 100644
--- a/drivers/mtd/nand/raw/mxc_nand.c
+++ b/drivers/mtd/nand/raw/mxc_nand.c
@@ -1575,6 +1575,23 @@ static int checkbad(struct mtd_info *mtd, loff_t ofs)
 		return ret;
 	}
 
+	/*
+	 * Automatically adding a BBT based on factory BBTs is only
+	 * sensible if the NAND is pristine. Abort if the first page
+	 * looks like a bootloader or UBI block.
+	 */
+	if (is_barebox_arm_head(buf)) {
+		dev_err(mtd->dev.parent,
+			"Flash seems to contain a barebox image, refusing to create BBT\n");
+		return -EINVAL;
+	}
+
+	if (!memcmp(buf, "UBI#", 4)) {
+		dev_err(mtd->dev.parent,
+			"Flash seems to contain a UBI, refusing to create BBT\n");
+		return -EINVAL;
+	}
+
 	if (buf[2000] != 0xff)
 		/* block considered bad */
 		return 1;
-- 
2.43.0