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, 3 insertions, 0 deletions

diff --git a/include/linux/mtd/nand.h b/include/linux/mtd/nand.h
index 1482340d3d9f..2829e8be3a62 100644
--- a/include/linux/mtd/nand.h
+++ b/include/linux/mtd/nand.h
@@ -459,6 +459,8 @@ struct nand_buffers {
  * @pagemask:           [INTERN] page number mask = number of (pages / chip) - 1
  * @pagebuf:            [INTERN] holds the pagenumber which is currently in
  *                      data_buf.
+ * @pagebuf_bitflips:   [INTERN] holds the bitflip count for the page which is
+ *                      currently in data_buf.
  * @subpagesize:        [INTERN] holds the subpagesize
  * @onfi_version:       [INTERN] holds the chip ONFI version (BCD encoded),
  *                      non 0 if ONFI supported.
@@ -519,6 +521,7 @@ struct nand_chip {
         uint64_t chipsize;
         int pagemask;
         int pagebuf;
+        unsigned int pagebuf_bitflips;
         int subpagesize;
         uint8_t cellinfo;
         int badblockpos;