mtd: nand: atmel: correct bitflips in erased pages for pre-sama5d4 SoCs

New atmel SoCs are able to fix bitflips in erased pages, but old ones
are still impacted by this problem. Use nand_check_erased_ecc_chunk() to
handle this case.
Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>
Reported-by: Herve Codina <herve.CODINA@celad.com>
Reviewed-by: Herve Codina <herve.CODINA@celad.com>
Tested-by: Herve Codina <herve.CODINA@celad.com>

drivers/mtd/nand/atmel_nand.c

@@ -863,17 +863,6 @@ static int pmecc_correction(struct mtd_info *mtd, u32 pmecc_stat, uint8_t *buf,
 	uint8_t *buf_pos;
 	int max_bitflips = 0;
 
-	/* If can correct bitfilps from erased page, do the normal check */
-	if (host->caps->pmecc_correct_erase_page)
-		goto normal_check;
-
-	for (i = 0; i < nand_chip->ecc.total; i++)
-		if (ecc[i] != 0xff)
-			goto normal_check;
-	/* Erased page, return OK */
-	return 0;
-
-normal_check:
 	for (i = 0; i < nand_chip->ecc.steps; i++) {
 		err_nbr = 0;
 		if (pmecc_stat & 0x1) {
@@ -884,17 +873,31 @@ static int pmecc_correction(struct mtd_info *mtd, u32 pmecc_stat, uint8_t *buf,
 			pmecc_get_sigma(mtd);
 
 			err_nbr = pmecc_err_location(mtd);
-			if (err_nbr == -1) {
+			if (err_nbr >= 0) {
+				pmecc_correct_data(mtd, buf_pos, ecc, i,
+						   nand_chip->ecc.bytes,
+						   err_nbr);
+			} else if (!host->caps->pmecc_correct_erase_page) {
+				u8 *ecc_pos = ecc + (i * nand_chip->ecc.bytes);
+
+				/* Try to detect erased pages */
+				err_nbr = nand_check_erased_ecc_chunk(buf_pos,
+							host->pmecc_sector_size,
+							ecc_pos,
+							nand_chip->ecc.bytes,
+							NULL, 0,
+							nand_chip->ecc.strength);
+			}
+
+			if (err_nbr < 0) {
 				dev_err(host->dev, "PMECC: Too many errors\n");
 				mtd->ecc_stats.failed++;
 				return -EIO;
-			} else {
-				pmecc_correct_data(mtd, buf_pos, ecc, i,
-					nand_chip->ecc.bytes, err_nbr);
+			}
+
 			mtd->ecc_stats.corrected += err_nbr;
 			max_bitflips = max_t(int, max_bitflips, err_nbr);
 		}
-		}
 		pmecc_stat >>= 1;
 	}