mtd: check for max_bitflips in mtd_read_oob()

mtd_read_oob() has some unexpected similarities to mtd_read(). For
instance, when ops->datbuf != NULL, nand_base.c might return max_bitflips;
however, when ops->datbuf == NULL, nand_base's code potentially could
return -EUCLEAN (no in-tree drivers do this yet). In any case where the
driver might return max_bitflips, we should translate this into an
appropriate return code using the bitflip_threshold.

Essentially, mtd_read_oob() duplicates the logic from mtd_read().

This prevents users of mtd_read_oob() from receiving a positive return
value (i.e., from max_bitflips) and interpreting it as an unknown error.

Artem: amend comments.

Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Reviewed-by: Mike Dunn <mikedunn@newsguy.com>
Reviewed-by: Shmulik Ladkani <shmulik.ladkani@gmail.com>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>

1 files changed, 13 insertions, 1 deletions

diff --git a/drivers/mtd/mtdcore.c b/drivers/mtd/mtdcore.c
index fcfce24f87d1..ec794a72975d 100644
--- a/drivers/mtd/mtdcore.c
+++ b/drivers/mtd/mtdcore.c
@@ -860,10 +860,22 @@ EXPORT_SYMBOL_GPL(mtd_panic_write);
 
 int mtd_read_oob(struct mtd_info *mtd, loff_t from, struct mtd_oob_ops *ops)
 {
+        int ret_code;
         ops->retlen = ops->oobretlen = 0;
         if (!mtd->_read_oob)
                 return -EOPNOTSUPP;
-        return mtd->_read_oob(mtd, from, ops);
+        /*
+         * In cases where ops->datbuf != NULL, mtd->_read_oob() has semantics
+         * similar to mtd->_read(), returning a non-negative integer
+         * representing max bitflips. In other cases, mtd->_read_oob() may
+         * return -EUCLEAN. In all cases, perform similar logic to mtd_read().
+         */
+        ret_code = mtd->_read_oob(mtd, from, ops);
+        if (unlikely(ret_code < 0))
+                return ret_code;
+        if (mtd->ecc_strength == 0)
+                return 0;       /* device lacks ecc */
+        return ret_code >= mtd->bitflip_threshold ? -EUCLEAN : 0;
 }
 EXPORT_SYMBOL_GPL(mtd_read_oob);