mtd: adapt writebufsize calculation for concat

If different chips with different writebufsize are concatenated,
the writebufsize from the concat device has to be taken from
the device with the largest writebuffer. This writebufsize
is used later on in the UBI layer for the min I/O size.
Signed-off-by: Holger Brunck <holger.brunck@keymile.com>
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>

drivers/mtd/mtdconcat.c

@@ -750,6 +750,7 @@ struct mtd_info *mtd_concat_create(struct mtd_info *subdev[],	/* subdevices to c
 	struct mtd_concat *concat;
 	uint32_t max_erasesize, curr_erasesize;
 	int num_erase_region;
+	int max_writebufsize = 0;
 
 	printk(KERN_NOTICE "Concatenating MTD devices:\n");
 	for (i = 0; i < num_devs; i++)
@@ -776,7 +777,12 @@ struct mtd_info *mtd_concat_create(struct mtd_info *subdev[],	/* subdevices to c
 	concat->mtd.size = subdev[0]->size;
 	concat->mtd.erasesize = subdev[0]->erasesize;
 	concat->mtd.writesize = subdev[0]->writesize;
-	concat->mtd.writebufsize = subdev[0]->writebufsize;
+
+	for (i = 0; i < num_devs; i++)
+		if (max_writebufsize < subdev[i]->writebufsize)
+			max_writebufsize = subdev[i]->writebufsize;
+	concat->mtd.writebufsize = max_writebufsize;
+
 	concat->mtd.subpage_sft = subdev[0]->subpage_sft;
 	concat->mtd.oobsize = subdev[0]->oobsize;
 	concat->mtd.oobavail = subdev[0]->oobavail;