[PATCH 5/5] nand: mxs: Fix for calculating ecc strength on some types of NAND flash

[Dmitry Lavnikevich]

Was tested on NAND with {writesize=4096, oobsize=224} and
{writesize=2048, oobsize=64}.

This patch will not break any NAND that was working
before. Implemented calculation way may be used for other NAND chips
with writesize == 2048 but oobsize != 64.

Signed-off-by: Dmitry Lavnikevich <d.lavnikevich at sam-solutions.com>
Signed-off-by: Grigory Milev <g.milev at sam-solutions.com>
---
 drivers/mtd/nand/nand_mxs.c | 21 +++++++++++++++++----
 1 file changed, 17 insertions(+), 4 deletions(-)

diff --git a/drivers/mtd/nand/nand_mxs.c b/drivers/mtd/nand/nand_mxs.c
index 237a423..b06b558 100644
--- a/drivers/mtd/nand/nand_mxs.c
+++ b/drivers/mtd/nand/nand_mxs.c
@@ -234,18 +234,31 @@ static uint32_t mxs_nand_aux_status_offset(void)
 static inline uint32_t mxs_nand_get_ecc_strength(uint32_t page_data_size,
 						uint32_t page_oob_size)
 {
+	int ecc_chunk_count = mxs_nand_ecc_chunk_cnt(page_data_size);
+	int ecc_strength = 0;
+	int gf_len = 13;  /* length of Galois Field for non-DDR nand */
+
+	/*
+	 * Possibly this if-else calculation may be removed since
+	 * ecc_strength calculated after it is taken from kernel driver
+	 * and therefore should work for all cases. But it was tested only
+	 * on devices with {data_size = 2046, oob_size = 64} and
+	 * {data_size = 4096, oob_size = 224} configuration.
+	 */
 	if (page_data_size == 2048)
 		return 8;
-
-	if (page_data_size == 4096) {
+	else if (page_data_size == 4096) {
 		if (page_oob_size == 128)
 			return 8;
-
 		if (page_oob_size == 218)
 			return 16;
 	}
 
-	return 0;
+	ecc_strength = ((page_oob_size - MXS_NAND_METADATA_SIZE) * 8)
+		/ (gf_len * ecc_chunk_count);
+
+	/* We need the minor even number. */
+	return rounddown(ecc_strength, 2);
 }
 
 static inline uint32_t mxs_nand_get_mark_offset(uint32_t page_data_size,
-- 
1.9.0