rtc: at91rm9200: fix reading alarm value

When alarm value is read at boot time, at91_alarm_year is not yet set to
the proper value so the year is always set to 1900.

This results in that kind of message at boot:
rtc rtc0: invalid alarm value: 1900-1-14 2:11:39

There is no way to recover from that as the alarm is now only read when
booting.

Instead, rely on the rtc core to figure out the proper year.

Acked-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>

drivers/rtc/rtc-at91rm9200.c

@@ -42,8 +42,6 @@
 #define at91_rtc_write(field, val) \
 	writel_relaxed((val), at91_rtc_regs + field)
 
-#define AT91_RTC_EPOCH		1900UL	/* just like arch/arm/common/rtctime.c */
-
 struct at91_rtc_config {
 	bool use_shadow_imr;
 };
@@ -51,7 +49,6 @@ struct at91_rtc_config {
 static const struct at91_rtc_config *at91_rtc_config;
 static DECLARE_COMPLETION(at91_rtc_updated);
 static DECLARE_COMPLETION(at91_rtc_upd_rdy);
-static unsigned int at91_alarm_year = AT91_RTC_EPOCH;
 static void __iomem *at91_rtc_regs;
 static int irq;
 static DEFINE_SPINLOCK(at91_rtc_lock);
@@ -131,8 +128,7 @@ static void at91_rtc_decodetime(unsigned int timereg, unsigned int calreg,
 
 	/*
 	 * The Calendar Alarm register does not have a field for
-	 * the year - so these will return an invalid value.  When an
-	 * alarm is set, at91_alarm_year will store the current year.
+	 * the year - so these will return an invalid value.
 	 */
 	tm->tm_year  = bcd2bin(date & AT91_RTC_CENT) * 100;	/* century */
 	tm->tm_year += bcd2bin((date & AT91_RTC_YEAR) >> 8);	/* year */
@@ -208,14 +204,14 @@ static int at91_rtc_readalarm(struct device *dev, struct rtc_wkalrm *alrm)
 	struct rtc_time *tm = &alrm->time;
 
 	at91_rtc_decodetime(AT91_RTC_TIMALR, AT91_RTC_CALALR, tm);
-	tm->tm_year = at91_alarm_year - 1900;
+	tm->tm_year = -1;
 
 	alrm->enabled = (at91_rtc_read_imr() & AT91_RTC_ALARM)
 			? 1 : 0;
 
-	dev_dbg(dev, "%s(): %4d-%02d-%02d %02d:%02d:%02d\n", __func__,
-		1900 + tm->tm_year, tm->tm_mon, tm->tm_mday,
-		tm->tm_hour, tm->tm_min, tm->tm_sec);
+	dev_dbg(dev, "%s(): %02d-%02d %02d:%02d:%02d %sabled\n", __func__,
+		tm->tm_mon, tm->tm_mday, tm->tm_hour, tm->tm_min, tm->tm_sec,
+		alrm->enabled ? "en" : "dis");
 
 	return 0;
 }
@@ -229,8 +225,6 @@ static int at91_rtc_setalarm(struct device *dev, struct rtc_wkalrm *alrm)
 
 	at91_rtc_decodetime(AT91_RTC_TIMR, AT91_RTC_CALR, &tm);
 
-	at91_alarm_year = tm.tm_year;
-
 	tm.tm_mon = alrm->time.tm_mon;
 	tm.tm_mday = alrm->time.tm_mday;
 	tm.tm_hour = alrm->time.tm_hour;
@@ -254,7 +248,7 @@ static int at91_rtc_setalarm(struct device *dev, struct rtc_wkalrm *alrm)
 	}
 
 	dev_dbg(dev, "%s(): %4d-%02d-%02d %02d:%02d:%02d\n", __func__,
-		at91_alarm_year, tm.tm_mon, tm.tm_mday, tm.tm_hour,
+		tm.tm_year, tm.tm_mon, tm.tm_mday, tm.tm_hour,
 		tm.tm_min, tm.tm_sec);
 
 	return 0;