mtd: rawnand: stm32_fmc2: fix ECC overwrite

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: 2cd457f ("mtd: rawnand: stm32_fmc2: add STM32 FMC2 NAND flash controller driver")
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>

Author: Christophe Kerello

drivers/mtd/nand/raw/stm32_fmc2_nand.c

@@ -985,9 +985,21 @@ 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;
 	}