rtc: refine rtc_timer_do_work() to consider other set alarm failures

rtc_timer_do_work() only judges -ETIME failure of__rtc_set_alarm(), but
doesn't handle other failures like -EIO, -EBUSY, etc.

If there is a failure other than -ETIME, the next rtc_timer will stay in
the timerqueue.  Then later rtc_timers will be enqueued directly because
they have a later expires time, so the alarm irq will never be programmed.

When such failures happen, this patch will retry __rtc_set_alarm(), if
still can't program the alarm time, it will remove current rtc_timer from
timerqueue and fetch next one, thus preventing it from affecting other rtc
timers.
Signed-off-by: Xunlei Pang <pang.xunlei@linaro.org>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Arnd Bergmann <arnd.bergmann@linaro.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/rtc/interface.c

@@ -899,11 +899,24 @@ void rtc_timer_do_work(struct work_struct *work)
 	if (next) {
 		struct rtc_wkalrm alarm;
 		int err;
+		int retry = 3;
+
 		alarm.time = rtc_ktime_to_tm(next->expires);
 		alarm.enabled = 1;
+reprogram:
 		err = __rtc_set_alarm(rtc, &alarm);
 		if (err == -ETIME)
 			goto again;
+		else if (err) {
+			if (retry-- > 0)
+				goto reprogram;
+
+			timer = container_of(next, struct rtc_timer, node);
+			timerqueue_del(&rtc->timerqueue, &timer->node);
+			timer->enabled = 0;
+			dev_err(&rtc->dev, "__rtc_set_alarm: err=%d\n", err);
+			goto again;
+		}
 	} else
 		rtc_alarm_disable(rtc);