mtd: rawnand: check return code of nand_reset() and nand_readid_op()

nand_scan_ident() iterates over maxchips to find as many homogeneous
chips as possible.

Since commit 2d472aba ("mtd: nand: document the NAND
controller/NAND chip DT representation"), new drivers should pass in
the exact number of CS lines instead of possible max, but old
platforms may still rely on nand_scan_ident() to detect the actual
number of connected CS lines.

In that case, this loop bails out when manufacturer or device ID
unmatches. The reason of unmatch is most likely no chip is connected
to that CS line. If so, nand_reset() should already have failed,
and the following nand_readid_op() is pointless.

Before ->exec_op hook was introduced, drivers had no way to tell
the failure of NAND_CMD_RESET to the framework because the legacy
->cmdfunc() has void return type. Now drivers implementing ->exec_op
hook can return the error code. You can save nand_readid_op() by
checking the return value of nand_reset(). The return value of
nand_readid_op() should be checked as well. If it fails, probably
id[0] and id[1] are undefined values.

Just for consistency, it should be sensible to check the return
code in nand_do_write_oob() as well.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Boris Brezillon <bbrezillon@kernel.org>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>

drivers/mtd/nand/raw/nand_base.c

@@ -420,7 +420,7 @@ static int nand_do_write_oob(struct nand_chip *chip, loff_t to,
 			     struct mtd_oob_ops *ops)
 {
 	struct mtd_info *mtd = nand_to_mtd(chip);
-	int chipnr, page, status, len;
+	int chipnr, page, status, len, ret;
 
 	pr_debug("%s: to = 0x%08x, len = %i\n",
 			 __func__, (unsigned int)to, (int)ops->ooblen);
@@ -442,7 +442,9 @@ static int nand_do_write_oob(struct nand_chip *chip, loff_t to,
 	 * if we don't do this. I have no clue why, but I seem to have 'fixed'
 	 * it in the doc2000 driver in August 1999.  dwmw2.
 	 */
-	nand_reset(chip, chipnr);
+	ret = nand_reset(chip, chipnr);
+	if (ret)
+		return ret;
 
 	nand_select_target(chip, chipnr);
 
@@ -5019,11 +5021,15 @@ static int nand_scan_ident(struct nand_chip *chip, unsigned int maxchips,
 		u8 id[2];
 
 		/* See comment in nand_get_flash_type for reset */
-		nand_reset(chip, i);
+		ret = nand_reset(chip, i);
+		if (ret)
+			break;
 
 		nand_select_target(chip, i);
 		/* Send the command for reading device ID */
-		nand_readid_op(chip, 0, id, sizeof(id));
+		ret = nand_readid_op(chip, 0, id, sizeof(id));
+		if (ret)
+			break;
 		/* Read manufacturer and device IDs */
 		if (nand_maf_id != id[0] || nand_dev_id != id[1]) {
 			nand_deselect_target(chip);