mtd: nand: handle ECC errors in OOB

While the standard NAND OOB functions do not do ECC on the spare area,
it is possible for a driver to supply its own OOB ECC functions (e.g., HW
ECC). nand_do_read_oob should act like nand_do_read_ops in checking the
ECC stats and returning -EBADMSG or -EUCLEAN on uncorrectable errors or
correctable bitflips, respectively. These error codes could be used in
flash-based BBT code or in YAFFS, for example.

Doing this, however, messes with the behavior of mtd_do_readoob. Now,
mtd_do_readoob should check whether we had -EUCLEAN or -EBADMSG errors
and discard those as "non-fatal" so that the ioctls can still succeed
with (possibly uncorrected) data.

Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>

1 files changed, 15 insertions, 0 deletions

diff --git a/drivers/mtd/mtdchar.c b/drivers/mtd/mtdchar.c
index c60067b1f07a..d5924635ead5 100644
--- a/drivers/mtd/mtdchar.c
+++ b/drivers/mtd/mtdchar.c
@@ -473,6 +473,21 @@ static int mtd_do_readoob(struct mtd_info *mtd, uint64_t start,
 		ret = -EFAULT;
 
 	kfree(ops.oobbuf);
+
+	/*
+	 * NAND returns -EBADMSG on ECC errors, but it returns the OOB
+	 * data. For our userspace tools it is important to dump areas
+	 * with ECC errors!
+	 * For kernel internal usage it also might return -EUCLEAN
+	 * to signal the caller that a bitflip has occured and has
+	 * been corrected by the ECC algorithm.
+	 *
+	 * Note: most NAND ECC algorithms do not calculate ECC
+	 * for the OOB area.
+	 */
+	if (ret == -EUCLEAN || ret == -EBADMSG)
+		return 0;
+
 	return ret;
 }