mtd: rawnand: Ensure the number of bitflips is consistent

The main NAND read page function can loop over "page reads" many times
in if the reading reports uncorrectable error(s) and if the chip
supports the read_retry feature.

In this case, the number of bitflips is summarized between
attempts. Fix this by re-initializing the entire mtd_ecc_stats object
each time we retry.
Suggested-by: Boris Brezillon <boris.brezillon@collabora.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Link: https://lore.kernel.org/linux-mtd/20200519074549.23673-4-miquel.raynal@bootlin.com

drivers/mtd/nand/raw/nand_base.c

@@ -3295,7 +3295,7 @@ static int nand_do_read_ops(struct nand_chip *chip, loff_t from,
 	oob_required = oob ? 1 : 0;
 
 	while (1) {
-		unsigned int ecc_failures = mtd->ecc_stats.failed;
+		struct mtd_ecc_stats ecc_stats = mtd->ecc_stats;
 
 		bytes = min(mtd->writesize - col, readlen);
 		aligned = (bytes == mtd->writesize);
@@ -3346,7 +3346,7 @@ static int nand_do_read_ops(struct nand_chip *chip, loff_t from,
 			 */
 			if (use_bounce_buf) {
 				if (!NAND_HAS_SUBPAGE_READ(chip) && !oob &&
-				    !(mtd->ecc_stats.failed - ecc_failures) &&
+				    !(mtd->ecc_stats.failed - ecc_stats.failed) &&
 				    (ops->mode != MTD_OPS_RAW)) {
 					chip->pagecache.page = realpage;
 					chip->pagecache.bitflips = ret;
@@ -3369,7 +3369,7 @@ static int nand_do_read_ops(struct nand_chip *chip, loff_t from,
 
 			nand_wait_readrdy(chip);
 
-			if (mtd->ecc_stats.failed - ecc_failures) {
+			if (mtd->ecc_stats.failed - ecc_stats.failed) {
 				if (retry_mode + 1 < chip->read_retries) {
 					retry_mode++;
 					ret = nand_setup_read_retry(chip,
@@ -3377,8 +3377,8 @@ static int nand_do_read_ops(struct nand_chip *chip, loff_t from,
 					if (ret < 0)
 						break;
 
-					/* Reset failures; retry */
-					mtd->ecc_stats.failed = ecc_failures;
+					/* Reset ecc_stats; retry */
+					mtd->ecc_stats = ecc_stats;
 					goto read_retry;
 				} else {
 					/* No more retry modes; real failure */