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>

2 files changed, 23 insertions, 1 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;
 }
 
diff --git a/drivers/mtd/nand/nand_base.c b/drivers/mtd/nand/nand_base.c
index 237d7daa189c..5418d27122c4 100644
--- a/drivers/mtd/nand/nand_base.c
+++ b/drivers/mtd/nand/nand_base.c
@@ -1750,6 +1750,7 @@ static int nand_do_read_oob(struct mtd_info *mtd, loff_t from,
 {
         int page, realpage, chipnr, sndcmd = 1;
         struct nand_chip *chip = mtd->priv;
+        struct mtd_ecc_stats stats;
         int blkcheck = (1 << (chip->phys_erase_shift - chip->page_shift)) - 1;
         int readlen = ops->ooblen;
         int len;
@@ -1758,6 +1759,8 @@ static int nand_do_read_oob(struct mtd_info *mtd, loff_t from,
         DEBUG(MTD_DEBUG_LEVEL3, "%s: from = 0x%08Lx, len = %i\n",
                         __func__, (unsigned long long)from, readlen);
 
+        stats = mtd->ecc_stats;
+
         if (ops->mode == MTD_OOB_AUTO)
                 len = chip->ecc.layout->oobavail;
         else
@@ -1828,7 +1831,11 @@ static int nand_do_read_oob(struct mtd_info *mtd, loff_t from,
         }
 
         ops->oobretlen = ops->ooblen;
-        return 0;
+
+        if (mtd->ecc_stats.failed - stats.failed)
+                return -EBADMSG;
+
+        return  mtd->ecc_stats.corrected - stats.corrected ? -EUCLEAN : 0;
 }
 
 /**