In case OOB write is requested during a data write, ECC is currently
lost. Avoid this issue by only writing in the free spare area.
This issue has been seen with a YAFFS2 file system.

Signed-off-by: Christophe Kerello <christophe.kerello@foss.st.com>
Cc: stable@vger.kernel.org
Fixes: 2cd457f328c1 ("mtd: rawnand: stm32_fmc2: add STM32 FMC2 NAND flash controller driver")
---
 drivers/mtd/nand/raw/stm32_fmc2_nand.c | 18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)

diff --git a/drivers/mtd/nand/raw/stm32_fmc2_nand.c b/drivers/mtd/nand/raw/stm32_fmc2_nand.c
index a960403081f11091837b73b8610231fe421d0c05..f84f23392fa441327bec90ba12a2a57d825d9330 100644
--- a/drivers/mtd/nand/raw/stm32_fmc2_nand.c
+++ b/drivers/mtd/nand/raw/stm32_fmc2_nand.c
@@ -996,9 +996,21 @@ static int stm32_fmc2_nfc_seq_write(struct nand_chip *chip, const u8 *buf,
 
 	/* Write oob */
 	if (oob_required) {
-		ret = nand_change_write_column_op(chip, mtd->writesize,
-						  chip->oob_poi, mtd->oobsize,
-						  false);
+		unsigned int offset_in_page = mtd->writesize;
+		const void *buf = chip->oob_poi;
+		unsigned int len = mtd->oobsize;
+
+		if (!raw) {
+			struct mtd_oob_region oob_free;
+
+			mtd_ooblayout_free(mtd, 0, &oob_free);
+			offset_in_page += oob_free.offset;
+			buf += oob_free.offset;
+			len = oob_free.length;
+		}
+
+		ret = nand_change_write_column_op(chip, offset_in_page,
+						  buf, len, false);
 		if (ret)
 			return ret;
 	}

---
base-commit: fb2fae70e7e985c4acb1ad96110d8b98bb64a87c
change-id: 20250811-fix-ecc-overwrite-9962b7797746

Best regards,
-- 
Christophe Kerello <christophe.kerello@foss.st.com>

On Tue, 12 Aug 2025 09:30:08 +0200, Christophe Kerello wrote:
> In case OOB write is requested during a data write, ECC is currently
> lost. Avoid this issue by only writing in the free spare area.
> This issue has been seen with a YAFFS2 file system.
> 
> 

Applied to mtd/fixes, thanks!

[1/1] mtd: rawnand: stm32_fmc2: fix ECC overwrite
      commit: 811c0da4542df3c065f6cb843ced68780e27bb44

Patche(s) should be available on mtd/linux.git and will be
part of the next PR (provided that no robot complains by then).

Kind regards,
Miquèl