[PATCH] nand_base: fix regression on nand with 64/128 oob size

[Alexander Couzens]

41b207a70d3a accidently changed the oob layout for nand when ECC doesn't use
the full available ecc reserved data.
This only affects controllers which use the default large page ops
nand_ooblayout_ecc_lp.

E.g. for davinci:
- nand has 2048 byte page, 64 byte oob
- 3 byte ecc every 512 byte using 1bit hw ecc
- requires 12 byte of oob space for ecc
- old layout reserved 24 byte based on 64 byte oob

Old layout started using byte from offset 40 while new layout
uses the last X bytes so it fits into the end of oob.
Meaning in this example the old layout uses byte 40-51, while
the new layout use byte 52-63.

Signed-off-by: Alexander Couzens <lynxis at fe80.eu>
---
 drivers/mtd/nand/nand_base.c | 19 ++++++++++++++++++-
 1 file changed, 18 insertions(+), 1 deletion(-)

diff --git a/drivers/mtd/nand/nand_base.c b/drivers/mtd/nand/nand_base.c
index b0524f8accb6..ba88345fd334 100644
--- a/drivers/mtd/nand/nand_base.c
+++ b/drivers/mtd/nand/nand_base.c
@@ -112,8 +112,25 @@ static int nand_ooblayout_ecc_lp(struct mtd_info *mtd, int section,
 	if (section)
 		return -ERANGE;
 
+	/* to be compatible with previous layouts
+	 * 64 byte oob must have ecc data at byte 40,
+	 * 128 byte oob must have ecc data at byte 80 */
+	switch (mtd->oobsize) {
+	case 64:
+		oobregion->offset = 40;
+		break;
+	case 128:
+		oobregion->offset = 80;
+		break;
+	default:
+		oobregion->offset = mtd->oobsize - oobregion->length;
+		break;
+	}
+
 	oobregion->length = ecc->total;
-	oobregion->offset = mtd->oobsize - oobregion->length;
+	if (oobregion->offset + oobregion->length > mtd->oobsize) {
+		return -ERANGE;
+	}
 
 	return 0;
 }
-- 
2.12.0