mtd: do not use mtd->read_*_prot_reg directly

Instead, call 'mtd_read_*_prot_info()' and check for -EOPNOTSUPP.
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>

drivers/mtd/mtdchar.c

@@ -366,20 +366,22 @@ static void mtdchar_erase_callback (struct erase_info *instr)
 static int otp_select_filemode(struct mtd_file_info *mfi, int mode)
 {
 	struct mtd_info *mtd = mfi->mtd;
+	size_t retlen;
 	int ret = 0;
 
+	/*
+	 * Make a fake call to mtd_read_fact_prot_reg() to check if OTP
+	 * operations are supported.
+	 */
+	if (mtd_read_fact_prot_reg(mtd, -1, -1, &retlen, NULL) == -EOPNOTSUPP)
+		return -EOPNOTSUPP;
+
 	switch (mode) {
 	case MTD_OTP_FACTORY:
-		if (!mtd->read_fact_prot_reg)
-			ret = -EOPNOTSUPP;
-		else
-			mfi->mode = MTD_FILE_MODE_OTP_FACTORY;
+		mfi->mode = MTD_FILE_MODE_OTP_FACTORY;
 		break;
 	case MTD_OTP_USER:
-		if (!mtd->read_fact_prot_reg)
-			ret = -EOPNOTSUPP;
-		else
-			mfi->mode = MTD_FILE_MODE_OTP_USER;
+		mfi->mode = MTD_FILE_MODE_OTP_USER;
 		break;
 	default:
 		ret = -EINVAL;

include/linux/mtd/mtd.h

@@ -352,6 +352,8 @@ static inline int mtd_read_fact_prot_reg(struct mtd_info *mtd, loff_t from,
 					 u_char *buf)
 {
 	*retlen = 0;
+	if (!mtd->read_fact_prot_reg)
+		return -EOPNOTSUPP;
 	return mtd->read_fact_prot_reg(mtd, from, len, retlen, buf);
 }
 
@@ -369,6 +371,8 @@ static inline int mtd_read_user_prot_reg(struct mtd_info *mtd, loff_t from,
 					 u_char *buf)
 {
 	*retlen = 0;
+	if (!mtd->read_user_prot_reg)
+		return -EOPNOTSUPP;
 	return mtd->read_user_prot_reg(mtd, from, len, retlen, buf);
 }