mtd: rawnand: arasan: Include ECC syndrome along with in-band data while checking for ECC failure

Following an ECC failure condition upon page reads, we shall distinguish
between a real ECC failure and an empty page. This is handled with a call
to nand_check_erased_ecc_chunk() which looks at the data and counts the
number of bits which are not 'ones'. If we get less zeros than the ECC
strength, we assume the page was erased and we are in the presence of
natural bitflips. Otherwise, if we are above, we assume some data was
written and the ECC engine could not recover it all, so we report an ECC
failure.

In order for this logic to be as close as the reality as we can (this is
already a simplified condition but we can hardly be more precise), we
should check all the data that is covered by the ECC step not only the
in-band data, so we should also include the ECC syndrome in the check.

Fixes: 88ffef1 ("mtd: rawnand: arasan: Support the hardware BCH ECC engine")
Signed-off-by: Amit Kumar Mahapatra <amit.kumar-mahapatra@amd.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20230927055621.2906454-1-amit.kumar-mahapatra@amd.com

Author: Amit Kumar Mahapatra

drivers/mtd/nand/raw/arasan-nand-controller.c

@@ -481,7 +481,7 @@ static int anfc_read_page_hw_ecc(struct nand_chip *chip, u8 *buf,
 		}
 
 		bf = nand_check_erased_ecc_chunk(raw_buf, chip->ecc.size,
-						 NULL, 0, NULL, 0,
+						 anand->hw_ecc, chip->ecc.bytes, NULL, 0,
 						 chip->ecc.strength);
 		if (bf > 0) {
 			mtd->ecc_stats.corrected += bf;