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>

2 files changed, 16 insertions, 6 deletions

diff --git a/drivers/mtd/nand/alauda.c b/drivers/mtd/nand/alauda.c
index 4f20e1d8bef..60a0dfdb080 100644
--- a/drivers/mtd/nand/alauda.c
+++ b/drivers/mtd/nand/alauda.c
@@ -414,7 +414,7 @@ static int alauda_bounce_read(struct mtd_info *mtd, loff_t from, size_t len,
 	}
 	err = 0;
 	if (corrected)
-		err = -EUCLEAN;
+		err = 1;	/* return max_bitflips per ecc step */
 	if (uncorrected)
 		err = -EBADMSG;
 out:
@@ -446,7 +446,7 @@ static int alauda_read(struct mtd_info *mtd, loff_t from, size_t len,
 	}
 	err = 0;
 	if (corrected)
-		err = -EUCLEAN;
+		err = 1;	/* return max_bitflips per ecc step */
 	if (uncorrected)
 		err = -EBADMSG;
 	return err;
diff --git a/drivers/mtd/nand/nand_base.c b/drivers/mtd/nand/nand_base.c
index 9f5d339a361..640f1f8159e 100644
--- a/drivers/mtd/nand/nand_base.c
+++ b/drivers/mtd/nand/nand_base.c
@@ -1486,6 +1486,7 @@ static int nand_do_read_ops(struct mtd_info *mtd, loff_t from,
 		mtd->oobavail : mtd->oobsize;
 
 	uint8_t *bufpoi, *oob, *buf;
+	unsigned int max_bitflips = 0;
 
 	stats = mtd->ecc_stats;
 
@@ -1513,7 +1514,10 @@ static int nand_do_read_ops(struct mtd_info *mtd, loff_t from,
 				sndcmd = 0;
 			}
 
-			/* Now read the page into the buffer */
+			/*
+			 * Now read the page into the buffer.  Absent an error,
+			 * the read methods return max bitflips per ecc step.
+			 */
 			if (unlikely(ops->mode == MTD_OPS_RAW))
 				ret = chip->ecc.read_page_raw(mtd, chip,
 							      bufpoi, page);
@@ -1530,15 +1534,19 @@ static int nand_do_read_ops(struct mtd_info *mtd, loff_t from,
 				break;
 			}
 
+			max_bitflips = max_t(unsigned int, max_bitflips, ret);
+
 			/* Transfer not aligned data */
 			if (!aligned) {
 				if (!NAND_SUBPAGE_READ(chip) && !oob &&
 				    !(mtd->ecc_stats.failed - stats.failed) &&
-				    (ops->mode != MTD_OPS_RAW))
+				    (ops->mode != MTD_OPS_RAW)) {
 					chip->pagebuf = realpage;
-				else
+					chip->pagebuf_bitflips = ret;
+				} else {
 					/* Invalidate page cache */
 					chip->pagebuf = -1;
+				}
 				memcpy(buf, chip->buffers->databuf + col, bytes);
 			}
 
@@ -1571,6 +1579,8 @@ static int nand_do_read_ops(struct mtd_info *mtd, loff_t from,
 		} else {
 			memcpy(buf, chip->buffers->databuf + col, bytes);
 			buf += bytes;
+			max_bitflips = max_t(unsigned int, max_bitflips,
+					     chip->pagebuf_bitflips);
 		}
 
 		readlen -= bytes;
@@ -1609,7 +1619,7 @@ static int nand_do_read_ops(struct mtd_info *mtd, loff_t from,
 	if (mtd->ecc_stats.failed - stats.failed)
 		return -EBADMSG;
 
-	return  mtd->ecc_stats.corrected - stats.corrected ? -EUCLEAN : 0;
+	return max_bitflips;
 }
 
 /**