drivers/rtc/rtc-r9701.c: reset registers if invalid values are detected

hwclock refuses to set date/time if RTC registers contain invalid
values.  Check the date/time register values at probe time and
initialize them to make hwclock happy.
Signed-off-by: Andreas Dumberger <andreas.dumberger@tqs.de>
Signed-off-by: Anatolij Gustschin <agust@denx.de>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/rtc/rtc-r9701.c

@@ -122,6 +122,7 @@ static const struct rtc_class_ops r9701_rtc_ops = {
 static int __devinit r9701_probe(struct spi_device *spi)
 {
 	struct rtc_device *rtc;
+	struct rtc_time dt;
 	unsigned char tmp;
 	int res;
 
@@ -132,6 +133,27 @@ static int __devinit r9701_probe(struct spi_device *spi)
 		return -ENODEV;
 	}
 
+	/*
+	 * The device seems to be present. Now check if the registers
+	 * contain invalid values. If so, try to write a default date:
+	 * 2000/1/1 00:00:00
+	 */
+	r9701_get_datetime(&spi->dev, &dt);
+	if (rtc_valid_tm(&dt)) {
+		dev_info(&spi->dev, "trying to repair invalid date/time\n");
+		dt.tm_sec  = 0;
+		dt.tm_min  = 0;
+		dt.tm_hour = 0;
+		dt.tm_mday = 1;
+		dt.tm_mon  = 0;
+		dt.tm_year = 100;
+
+		if (r9701_set_datetime(&spi->dev, &dt)) {
+			dev_err(&spi->dev, "cannot repair RTC register\n");
+			return -ENODEV;
+		}
+	}
+
 	rtc = rtc_device_register("r9701",
 				&spi->dev, &r9701_rtc_ops, THIS_MODULE);
 	if (IS_ERR(rtc))