mtd: rawnand: Add an invalid ECC mode to discriminate with valid ones

NAND ECC modes (or providers) have their own enumeration but, unlike
their algorithms counterpart, there is no invalid or uninitialized
value to discriminate between an error and having chosen a no-ECC
situation. Add an "invalid" entry for this purpose.
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Link: https://lore.kernel.org/linux-mtd/20200526195633.11543-7-miquel.raynal@bootlin.com

drivers/mtd/nand/raw/nand_base.c

@@ -5022,7 +5022,7 @@ static int of_get_nand_ecc_mode(struct device_node *np)
 	if (err < 0)
 		return err;
 
-	for (i = 0; i < ARRAY_SIZE(nand_ecc_modes); i++)
+	for (i = NAND_ECC_NONE; i < ARRAY_SIZE(nand_ecc_modes); i++)
 		if (!strcasecmp(pm, nand_ecc_modes[i]))
 			return i;
 

include/linux/mtd/rawnand.h

@@ -84,6 +84,7 @@ struct nand_chip;
  * Constants for ECC_MODES
  */
 enum nand_ecc_mode {
+	NAND_ECC_INVALID,
 	NAND_ECC_NONE,
 	NAND_ECC_SOFT,
 	NAND_ECC_HW,