mtd: mtdoops: do not use mtd->panic_write directly

Instead of checking if 'mtd->panic_write' is defined, call 'mtd_panic_write()'
and check the error code - '-EOPNOTSUPP' will be returned if the function is
not defined.
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>

drivers/mtd/mtdoops.c

@@ -221,10 +221,14 @@ static void mtdoops_write(struct mtdoops_context *cxt, int panic)
 	hdr[0] = cxt->nextcount;
 	hdr[1] = MTDOOPS_KERNMSG_MAGIC;
 
-	if (panic)
+	if (panic) {
 		ret = mtd_panic_write(mtd, cxt->nextpage * record_size,
 				      record_size, &retlen, cxt->oops_buf);
-	else
+		if (ret == -EOPNOTSUPP) {
+			printk(KERN_ERR "mtdoops: Cannot write from panic without panic_write\n");
+			return;
+		}
+	} else
 		ret = mtd_write(mtd, cxt->nextpage * record_size,
 				record_size, &retlen, cxt->oops_buf);
 
@@ -330,13 +334,8 @@ static void mtdoops_do_dump(struct kmsg_dumper *dumper,
 	memcpy(dst + l1_cpy, s2 + s2_start, l2_cpy);
 
 	/* Panics must be written immediately */
-	if (reason != KMSG_DUMP_OOPS) {
-		if (!cxt->mtd->panic_write)
-			printk(KERN_ERR "mtdoops: Cannot write from panic without panic_write\n");
-		else
+	if (reason != KMSG_DUMP_OOPS)
 		mtdoops_write(cxt, 1);
-		return;
-	}
 
 	/* For other cases, schedule work to write it "nicely" */
 	schedule_work(&cxt->work_write);

include/linux/mtd/mtd.h

@@ -311,6 +311,8 @@ static inline int mtd_panic_write(struct mtd_info *mtd, loff_t to, size_t len,
 				  size_t *retlen, const u_char *buf)
 {
 	*retlen = 0;
+	if (!mtd->panic_write)
+		return -EOPNOTSUPP;
 	return mtd->panic_write(mtd, to, len, retlen, buf);
 }