mtd: atmel_nand: add a definition for the oob reserved bytes

It's better to use a macro instead of just a number.
Signed-off-by: NJosh Wu <josh.wu@atmel.com>
Signed-off-by: NBrian Norris <computersforpeace@gmail.com>

drivers/mtd/nand/atmel_nand.c

@@ -485,7 +485,7 @@ static void pmecc_config_ecc_layout(struct nand_ecclayout *layout,
 	for (i = 0; i < ecc_len; i++)
 		layout->eccpos[i] = oobsize - ecc_len + i;
 
-	layout->oobfree[0].offset = 2;
+	layout->oobfree[0].offset = PMECC_OOB_RESERVED_BYTES;
 	layout->oobfree[0].length =
 		oobsize - ecc_len - layout->oobfree[0].offset;
 }
@@ -1254,7 +1254,8 @@ static int atmel_pmecc_nand_init_params(struct platform_device *pdev,
 		nand_chip->ecc.steps = mtd->writesize / sector_size;
 		nand_chip->ecc.total = nand_chip->ecc.bytes *
 			nand_chip->ecc.steps;
-		if (nand_chip->ecc.total > mtd->oobsize - 2) {
+		if (nand_chip->ecc.total >
+				mtd->oobsize - PMECC_OOB_RESERVED_BYTES) {
 			dev_err(host->dev, "No room for ECC bytes\n");
 			err_no = -EINVAL;
 			goto err;

drivers/mtd/nand/atmel_nand_ecc.h

@@ -152,4 +152,7 @@
 /* Time out value for reading PMECC status register */
 #define PMECC_MAX_TIMEOUT_MS			100
 
+/* Reserved bytes in oob area */
+#define PMECC_OOB_RESERVED_BYTES		2
+
 #endif