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>
diff --git a/drivers/mtd/mtdchar.c b/drivers/mtd/mtdchar.c
index c60067b..d592463 100644
--- a/drivers/mtd/mtdchar.c
+++ b/drivers/mtd/mtdchar.c
@@ -473,6 +473,21 @@
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;
}