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>

diff --git a/drivers/mtd/mtdcore.c b/drivers/mtd/mtdcore.c
index fcfce24f87d1d8e75332cb26b6b22387ca8284bc..ec794a72975dd886205f2460e2eaba08089a8daf 100644 (file)
--- 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);