rtc: use set_mmss when set_time is not available

Drivers should only need to implement either set_mmss (counter based RTCs)
or set_time (most RTCs).  The RTC subsystem will handle them
appropriately.

Signed-off-by: Alessandro Zummo <a.zummo@towertech.it>
Cc: Kumar Gala <galak@kernel.crashing.org>
Cc: David Brownell <david-b@pacbell.net>
Cc: Lennert Buytenhek <buytenh@wantstofly.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/drivers/rtc/interface.c b/drivers/rtc/interface.c
index 50482d1..4348c4b 100644
--- a/drivers/rtc/interface.c
+++ b/drivers/rtc/interface.c
@@ -50,10 +50,15 @@
 
 	if (!rtc->ops)
 		err = -ENODEV;
-	else if (!rtc->ops->set_time)
-		err = -EINVAL;
-	else
+	else if (rtc->ops->set_time)
 		err = rtc->ops->set_time(rtc->dev.parent, tm);
+	else if (rtc->ops->set_mmss) {
+		unsigned long secs;
+		err = rtc_tm_to_time(tm, &secs);
+		if (err == 0)
+			err = rtc->ops->set_mmss(rtc->dev.parent, secs);
+	} else
+		err = -EINVAL;
 
 	mutex_unlock(&rtc->ops_lock);
 	return err;