mtd: rawnand: brcmnand: correctly verify erased pages

The current code checks that the whole OOB area is erased.
This is a problem when JFFS2 cleanmarkers are added to the OOB, since it will
fail due to the usable OOB bytes not being 0xff.
Correct this by only checking that data and ECC bytes aren't 0xff.

Fixes: 02b88eea ("mtd: brcmnand: Add check for erased page bitflips")
Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20200512082451.771212-1-noltari@gmail.com

drivers/mtd/nand/raw/brcmnand/brcmnand.c

@@ -2017,28 +2017,31 @@ static int brcmnand_read_by_pio(struct mtd_info *mtd, struct nand_chip *chip,
 static int brcmstb_nand_verify_erased_page(struct mtd_info *mtd,
 		  struct nand_chip *chip, void *buf, u64 addr)
 {
-	int i, sas;
-	void *oob = chip->oob_poi;
+	struct mtd_oob_region ecc;
+	int i;
 	int bitflips = 0;
 	int page = addr >> chip->page_shift;
 	int ret;
+	void *ecc_bytes;
 	void *ecc_chunk;
 
 	if (!buf)
 		buf = nand_get_data_buf(chip);
 
-	sas = mtd->oobsize / chip->ecc.steps;
-
 	/* read without ecc for verification */
 	ret = chip->ecc.read_page_raw(chip, buf, true, page);
 	if (ret)
 		return ret;
 
-	for (i = 0; i < chip->ecc.steps; i++, oob += sas) {
+	for (i = 0; i < chip->ecc.steps; i++) {
 		ecc_chunk = buf + chip->ecc.size * i;
-		ret = nand_check_erased_ecc_chunk(ecc_chunk,
-						  chip->ecc.size,
-						  oob, sas, NULL, 0,
+
+		mtd_ooblayout_ecc(mtd, i, &ecc);
+		ecc_bytes = chip->oob_poi + ecc.offset;
+
+		ret = nand_check_erased_ecc_chunk(ecc_chunk, chip->ecc.size,
+						  ecc_bytes, ecc.length,
+						  NULL, 0,
 						  chip->ecc.strength);
 		if (ret < 0)
 			return ret;