mtd: driver _read() returns max_bitflips; mtd_read() returns -EUCLEAN

The drivers' _read() method, absent an error, returns a non-negative integer
indicating the maximum number of bit errors that were corrected in any one
region comprising an ecc step.  MTD returns -EUCLEAN if this is >=
bitflip_threshold, 0 otherwise.  If bitflip_threshold is zero, the comparison is
not made since these devices lack ECC and always return zero in the non-error
case (thanks Brian)¹.  Note that this is a subtle change to the driver
interface.

This and the preceding patches in this set were tested with ubi on top of the
nandsim and docg4 devices, running the ubi test io_basic from mtd-utils.

¹ http://lists.infradead.org/pipermail/linux-mtd/2012-March/040468.html

Signed-off-by: Mike Dunn <mikedunn@newsguy.com>
Acked-by: Robert Jarzmik <robert.jarzmik@free.fr>
Acked-by: Brian Norris <computersforpeace@gmail.com>
Ivan Djelic <ivan.djelic@parrot.com>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>

Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>

1 files changed, 4 insertions, 2 deletions

diff --git a/drivers/mtd/devices/docg3.c b/drivers/mtd/devices/docg3.c
index 8272c02668d6..65d22a0439c6 100644
--- a/drivers/mtd/devices/docg3.c
+++ b/drivers/mtd/devices/docg3.c
@@ -850,6 +850,7 @@ static int doc_read_oob(struct mtd_info *mtd, loff_t from,
         u8 *buf = ops->datbuf;
         size_t len, ooblen, nbdata, nboob;
         u8 hwecc[DOC_ECC_BCH_SIZE], eccconf1;
+        int max_bitflips = 0;
 
         if (buf)
                 len = ops->len;
@@ -876,7 +877,7 @@ static int doc_read_oob(struct mtd_info *mtd, loff_t from,
         ret = 0;
         skip = from % DOC_LAYOUT_PAGE_SIZE;
         mutex_lock(&docg3->cascade->lock);
-        while (!ret && (len > 0 || ooblen > 0)) {
+        while (ret >= 0 && (len > 0 || ooblen > 0)) {
                 calc_block_sector(from - skip, &block0, &block1, &page, &ofs,
                         docg3->reliable);
                 nbdata = min_t(size_t, len, DOC_LAYOUT_PAGE_SIZE - skip);
@@ -936,7 +937,8 @@ static int doc_read_oob(struct mtd_info *mtd, loff_t from,
                         }
                         if (ret > 0) {
                                 mtd->ecc_stats.corrected += ret;
-                                ret = -EUCLEAN;
+                                max_bitflips = max(max_bitflips, ret);
+                                ret = max_bitflips;
                         }
                 }