[PATCH 3/3] mtd: 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 the first 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 | 58 ++++++++++++++++++---------------
 1 file changed, 31 insertions(+), 27 deletions(-)

diff --git a/drivers/mtd/nand/raw/mxc_nand.c b/drivers/mtd/nand/raw/mxc_nand.c
index a72275480144..fd5ae447a198 100644
--- a/drivers/mtd/nand/raw/mxc_nand.c
+++ b/drivers/mtd/nand/raw/mxc_nand.c
@@ -1555,30 +1555,6 @@ static const struct nand_controller_ops mxcnd_controller_ops = {
  * From this point on we can forget about the BBMs and rely completely
  * on the flash BBT.
  */
-static int checkbad(struct nand_chip *chip, loff_t ofs)
-{
-	struct mtd_info *mtd = nand_to_mtd(chip);
-	int ret;
-	uint8_t buf[mtd->writesize + mtd->oobsize];
-	struct mtd_oob_ops ops;
-
-	ops.mode = MTD_OPS_RAW;
-	ops.ooboffs = 0;
-	ops.datbuf = buf;
-	ops.len = mtd->writesize;
-	ops.oobbuf = buf + mtd->writesize;
-	ops.ooblen = mtd->oobsize;
-
-	ret = mtd_read_oob(mtd, ofs, &ops);
-	if (ret < 0)
-		return ret;
-
-	if (buf[2000] != 0xff)
-		return 1;
-
-	return 0;
-}
-
 static int imxnd_create_bbt(struct nand_chip *chip)
 {
 	struct mtd_info *mtd = nand_to_mtd(chip);
@@ -1598,12 +1574,40 @@ static int imxnd_create_bbt(struct nand_chip *chip)
 
 	for (i = 0; i < numblocks; ++i) {
 		loff_t ofs = i << chip->bbt_erase_shift;
+		uint8_t buf[mtd->writesize + mtd->oobsize];
+		struct mtd_oob_ops ops = {
+			.mode = MTD_OPS_RAW,
+			.ooboffs = 0,
+			.datbuf = buf,
+			.len = mtd->writesize,
+			.oobbuf = buf + mtd->writesize,
+			.ooblen = mtd->oobsize,
+		};
 
-		ret = checkbad(chip, ofs);
-		if (ret < 0)
+		ret = mtd_read_oob(mtd, ofs, &ops);
+		if (ret < 0) {
+			dev_err(mtd->dev.parent, "Failed to read page at 0x%08x\n", (unsigned int)ofs);
 			goto out;
+		}
 
-		if (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 (ofs == 0 && is_barebox_arm_head(buf)) {
+			dev_err(mtd->dev.parent, "Flash seems to contain a barebox image, refusing\n");
+			ret = -EINVAL;
+			goto out;
+		}
+
+		if (ofs == 0 && !memcmp(buf, "UBI#", 4)) {
+			dev_err(mtd->dev.parent, "Flash seems to contain a UBI, refusing\n");
+			ret = -EINVAL;
+			goto out;
+		}
+
+		if (buf[2000] != 0xff) {
 			bbt[i >> 2] |= 0x03 << (2 * (i & 0x3));
 			dev_info(mtd->dev.parent, "Bad eraseblock %d at 0x%08x\n",
 				 i, (unsigned int)ofs);
-- 
2.43.0