mtd: nand: Fix nand_do_read_oob() return value

commit 87e89ce8 upstream.

Starting from commit 041e4575 ("mtd: nand: handle ECC errors in
OOB"), nand_do_read_oob() (from the NAND core) did return 0 or a
negative error, and the MTD layer expected it.

However, the trend for the NAND layer is now to return an error or a
positive number of bitflips. Deciding which status to return to the user
belongs to the MTD layer.

Commit e47f6858 ("mtd: check for max_bitflips in mtd_read_oob()")
brought this logic to the mtd_read_oob() function while the return value
coming from nand_do_read_oob() (called by the ->_read_oob() hook) was
left unchanged.

Fixes: e47f6858 ("mtd: check for max_bitflips in mtd_read_oob()")
Signed-off-by: Miquel Raynal <miquel.raynal@free-electrons.com>
Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/mtd/nand/nand_base.c

@@ -2023,6 +2023,7 @@ static int nand_write_oob_syndrome(struct mtd_info *mtd,
 static int nand_do_read_oob(struct mtd_info *mtd, loff_t from,
 			    struct mtd_oob_ops *ops)
 {
+	unsigned int max_bitflips = 0;
 	int page, realpage, chipnr;
 	struct nand_chip *chip = mtd->priv;
 	struct mtd_ecc_stats stats;
@@ -2083,6 +2084,8 @@ static int nand_do_read_oob(struct mtd_info *mtd, loff_t from,
 				nand_wait_ready(mtd);
 		}
 
+		max_bitflips = max_t(unsigned int, max_bitflips, ret);
+
 		readlen -= len;
 		if (!readlen)
 			break;
@@ -2108,7 +2111,7 @@ static int nand_do_read_oob(struct mtd_info *mtd, loff_t from,
 	if (mtd->ecc_stats.failed - stats.failed)
 		return -EBADMSG;
 
-	return  mtd->ecc_stats.corrected - stats.corrected ? -EUCLEAN : 0;
+	return max_bitflips;
 }
 
 /**