mtd: nand: fsl_ifc: fix handing of bit flips in erased pages

If we see unrecoverable ECC error, we need to count number of bitflips
from all-ones and report correctable/uncorrectable according to
that. Otherwise we report ECC failed on erased flash with single bit error.
Signed-off-by: Pavel Machek <pavel@denx.de>
Reported-by: Darwin Dingel <Darwin.Dingel@alliedtelesis.co.nz>
Acked-by: Darwin Dingel <Darwin.Dingel@alliedtelesis.co.nz>
Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>

drivers/mtd/nand/fsl_ifc_nand.c

@@ -171,34 +171,6 @@ static void set_addr(struct mtd_info *mtd, int column, int page_addr, int oob)
 		ifc_nand_ctrl->index += mtd->writesize;
 }
 
-static int is_blank(struct mtd_info *mtd, unsigned int bufnum)
-{
-	struct nand_chip *chip = mtd_to_nand(mtd);
-	struct fsl_ifc_mtd *priv = nand_get_controller_data(chip);
-	u8 __iomem *addr = priv->vbase + bufnum * (mtd->writesize * 2);
-	u32 __iomem *mainarea = (u32 __iomem *)addr;
-	u8 __iomem *oob = addr + mtd->writesize;
-	struct mtd_oob_region oobregion = { };
-	int i, section = 0;
-
-	for (i = 0; i < mtd->writesize / 4; i++) {
-		if (__raw_readl(&mainarea[i]) != 0xffffffff)
-			return 0;
-	}
-
-	mtd_ooblayout_ecc(mtd, section++, &oobregion);
-	while (oobregion.length) {
-		for (i = 0; i < oobregion.length; i++) {
-			if (__raw_readb(&oob[oobregion.offset + i]) != 0xff)
-				return 0;
-		}
-
-		mtd_ooblayout_ecc(mtd, section++, &oobregion);
-	}
-
-	return 1;
-}
-
 /* returns nonzero if entire page is blank */
 static int check_read_ecc(struct mtd_info *mtd, struct fsl_ifc_ctrl *ctrl,
 			  u32 *eccstat, unsigned int bufnum)
@@ -274,16 +246,14 @@ static void fsl_ifc_run_command(struct mtd_info *mtd)
 			if (errors == 15) {
 				/*
 				 * Uncorrectable error.
-				 * OK only if the whole page is blank.
+				 * We'll check for blank pages later.
 				 *
 				 * We disable ECCER reporting due to...
 				 * erratum IFC-A002770 -- so report it now if we
 				 * see an uncorrectable error in ECCSTAT.
 				 */
-				if (!is_blank(mtd, bufnum))
-					ctrl->nand_stat |=
-						IFC_NAND_EVTER_STAT_ECCER;
-				break;
+				ctrl->nand_stat |= IFC_NAND_EVTER_STAT_ECCER;
+				continue;
 			}
 
 			mtd->ecc_stats.corrected += errors;
@@ -678,6 +648,39 @@ static int fsl_ifc_wait(struct mtd_info *mtd, struct nand_chip *chip)
 	return nand_fsr | NAND_STATUS_WP;
 }
 
+/*
+ * The controller does not check for bitflips in erased pages,
+ * therefore software must check instead.
+ */
+static int check_erased_page(struct nand_chip *chip, u8 *buf)
+{
+	struct mtd_info *mtd = nand_to_mtd(chip);
+	u8 *ecc = chip->oob_poi;
+	const int ecc_size = chip->ecc.bytes;
+	const int pkt_size = chip->ecc.size;
+	int i, res, bitflips = 0;
+	struct mtd_oob_region oobregion = { };
+
+	mtd_ooblayout_ecc(mtd, 0, &oobregion);
+	ecc += oobregion.offset;
+
+	for (i = 0; i < chip->ecc.steps; ++i) {
+		res = nand_check_erased_ecc_chunk(buf, pkt_size, ecc, ecc_size,
+						  NULL, 0,
+						  chip->ecc.strength);
+		if (res < 0)
+			mtd->ecc_stats.failed++;
+		else
+			mtd->ecc_stats.corrected += res;
+
+		bitflips = max(res, bitflips);
+		buf += pkt_size;
+		ecc += ecc_size;
+	}
+
+	return bitflips;
+}
+
 static int fsl_ifc_read_page(struct mtd_info *mtd, struct nand_chip *chip,
 			     uint8_t *buf, int oob_required, int page)
 {
@@ -689,8 +692,12 @@ static int fsl_ifc_read_page(struct mtd_info *mtd, struct nand_chip *chip,
 	if (oob_required)
 		fsl_ifc_read_buf(mtd, chip->oob_poi, mtd->oobsize);
 
-	if (ctrl->nand_stat & IFC_NAND_EVTER_STAT_ECCER)
-		dev_err(priv->dev, "NAND Flash ECC Uncorrectable Error\n");
+	if (ctrl->nand_stat & IFC_NAND_EVTER_STAT_ECCER) {
+		if (!oob_required)
+			fsl_ifc_read_buf(mtd, chip->oob_poi, mtd->oobsize);
+
+		return check_erased_page(chip, buf);
+	}
 
 	if (ctrl->nand_stat != IFC_NAND_EVTER_STAT_OPC)
 		mtd->ecc_stats.failed++;