mtd: nand: localize ECC failures per page

ECC failures can be tracked at the page level, not the do_read_ops level
(i.e., a potentially multi-page transaction).

This helps prepare for READ RETRY support.

Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Acked-by: Huang Shijie <b32955@freescale.com>

drivers/mtd/nand/nand_base.c

@@ -1422,7 +1422,6 @@ static int nand_do_read_ops(struct mtd_info *mtd, loff_t from,
 {
 	int chipnr, page, realpage, col, bytes, aligned, oob_required;
 	struct nand_chip *chip = mtd->priv;
-	struct mtd_ecc_stats stats;
 	int ret = 0;
 	uint32_t readlen = ops->len;
 	uint32_t oobreadlen = ops->ooblen;
@@ -1431,8 +1430,7 @@ static int nand_do_read_ops(struct mtd_info *mtd, loff_t from,
 
 	uint8_t *bufpoi, *oob, *buf;
 	unsigned int max_bitflips = 0;
-
-	stats = mtd->ecc_stats;
+	bool ecc_fail = false;
 
 	chipnr = (int)(from >> chip->chip_shift);
 	chip->select_chip(mtd, chipnr);
@@ -1447,6 +1445,8 @@ static int nand_do_read_ops(struct mtd_info *mtd, loff_t from,
 	oob_required = oob ? 1 : 0;
 
 	while (1) {
+		unsigned int ecc_failures = mtd->ecc_stats.failed;
+
 		bytes = min(mtd->writesize - col, readlen);
 		aligned = (bytes == mtd->writesize);
 
@@ -1483,7 +1483,7 @@ static int nand_do_read_ops(struct mtd_info *mtd, loff_t from,
 			/* Transfer not aligned data */
 			if (!aligned) {
 				if (!NAND_HAS_SUBPAGE_READ(chip) && !oob &&
-				    !(mtd->ecc_stats.failed - stats.failed) &&
+				    !(mtd->ecc_stats.failed - ecc_failures) &&
 				    (ops->mode != MTD_OPS_RAW)) {
 					chip->pagebuf = realpage;
 					chip->pagebuf_bitflips = ret;
@@ -1513,6 +1513,9 @@ static int nand_do_read_ops(struct mtd_info *mtd, loff_t from,
 				else
 					nand_wait_ready(mtd);
 			}
+
+			if (mtd->ecc_stats.failed - ecc_failures)
+				ecc_fail = true;
 		} else {
 			memcpy(buf, chip->buffers->databuf + col, bytes);
 			buf += bytes;
@@ -1547,7 +1550,7 @@ static int nand_do_read_ops(struct mtd_info *mtd, loff_t from,
 	if (ret < 0)
 		return ret;
 
-	if (mtd->ecc_stats.failed - stats.failed)
+	if (ecc_fail)
 		return -EBADMSG;
 
 	return max_bitflips;