Revert "rtc: pcf8523: properly handle oscillator stop bit"

This reverts commit ede44c9.

See: raspberrypi/firmware#1065

Signed-off-by: Phil Elwell <phil@raspberrypi.org>

drivers/rtc/rtc-pcf8523.c

@@ -178,8 +178,28 @@ static int pcf8523_rtc_read_time(struct device *dev, struct rtc_time *tm)
 	if (err < 0)
 		return err;
 
-	if (regs[0] & REG_SECONDS_OS)
-		return -EINVAL;
+	if (regs[0] & REG_SECONDS_OS) {
+		/*
+		 * If the oscillator was stopped, try to clear the flag. Upon
+		 * power-up the flag is always set, but if we cannot clear it
+		 * the oscillator isn't running properly for some reason. The
+		 * sensible thing therefore is to return an error, signalling
+		 * that the clock cannot be assumed to be correct.
+		 */
+
+		regs[0] &= ~REG_SECONDS_OS;
+
+		err = pcf8523_write(client, REG_SECONDS, regs[0]);
+		if (err < 0)
+			return err;
+
+		err = pcf8523_read(client, REG_SECONDS, &regs[0]);
+		if (err < 0)
+			return err;
+
+		if (regs[0] & REG_SECONDS_OS)
+			return -EAGAIN;
+	}
 
 	tm->tm_sec = bcd2bin(regs[0] & 0x7f);
 	tm->tm_min = bcd2bin(regs[1] & 0x7f);
@@ -215,7 +235,6 @@ static int pcf8523_rtc_set_time(struct device *dev, struct rtc_time *tm)
 		return err;
 
 	regs[0] = REG_SECONDS;
-	/* This will purposely overwrite REG_SECONDS_OS */
 	regs[1] = bin2bcd(tm->tm_sec);
 	regs[2] = bin2bcd(tm->tm_min);
 	regs[3] = bin2bcd(tm->tm_hour);