mtd: rawnand: brcmnand: fix OOB R/W with Hamming ECC

Hamming ECC doesn't cover the OOB data, so reading or writing OOB shall
always be done without ECC enabled.
This is a problem when adding JFFS2 cleanmarkers to erased blocks. If JFFS2
clenmarkers are added to the OOB with ECC enabled, OOB bytes will be changed
from ff ff ff to 00 00 00, reporting incorrect ECC errors.

Fixes: 27c5b17 ("mtd: nand: add NAND driver "library" for Broadcom STB NAND controller")
Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>
Acked-by: Brian Norris <computersforpeace@gmail.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20210224080210.23686-1-noltari@gmail.com

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

@@ -2688,6 +2688,12 @@ static int brcmnand_attach_chip(struct nand_chip *chip)
 
 	ret = brcmstb_choose_ecc_layout(host);
 
+	/* If OOB is written with ECC enabled it will cause ECC errors */
+	if (is_hamming_ecc(host->ctrl, &host->hwcfg)) {
+		chip->ecc.write_oob = brcmnand_write_oob_raw;
+		chip->ecc.read_oob = brcmnand_read_oob_raw;
+	}
+
 	return ret;
 }