drivers/rtc/rtc-m41t93.c: don't let get_time() reset M41T93_FLAG_OF

If the rtc reports the time might be invalid due to oscillator failure,
M41T93_FLAG_OF flag must not be reset by get_time() as the read operation
doesn't make the time valid.

Without this patch, only the first get_time() reported an invalid time,
the second get_time() reported a valid time althought the reported time is
probably wrong due to oscillator failure.

Instead of resetting in get_time(), with this patch M41T93_FLAG_OF is
reset in set_time() when a valid time is to be written.

Signed-off-by: Nikolaus Voss <[e-mail]>
Cc: Alessandro Zummo <[e-mail]>
Cc: Grant Likely <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

drivers/rtc/rtc-m41t93.c

···
 static int m41t93_set_time(struct device *dev, struct rtc_time *tm)
 {
 	struct spi_device *spi = to_spi_device(dev);
+	int tmp;
 	u8 buf[9] = {0x80};        /* write cmd + 8 data bytes */
 	u8 * const data = &buf[1]; /* ptr to first data byte */
 
···
 	if (tm->tm_year < 100) {
 		dev_warn(&spi->dev, "unsupported date (before 2000-01-01).\n");
 		return -EINVAL;
+	}
+
+	tmp = spi_w8r8(spi, M41T93_REG_FLAGS);
+	if (tmp < 0)
+		return tmp;
+
+	if (tmp & M41T93_FLAG_OF) {
+		dev_warn(&spi->dev, "OF bit is set, resetting.\n");
+		m41t93_set_reg(spi, M41T93_REG_FLAGS, tmp & ~M41T93_FLAG_OF);
+
+		tmp = spi_w8r8(spi, M41T93_REG_FLAGS);
+		if (tmp < 0) {
+			return tmp;
+		} else if (tmp & M41T93_FLAG_OF) {
+			/* OF cannot be immediately reset: oscillator has to be
+			 * restarted. */
+			u8 reset_osc = buf[M41T93_REG_ST_SEC] | M41T93_FLAG_ST;
+
+			dev_warn(&spi->dev,
+				 "OF bit is still set, kickstarting clock.\n");
+			m41t93_set_reg(spi, M41T93_REG_ST_SEC, reset_osc);
+			reset_osc &= ~M41T93_FLAG_ST;
+			m41t93_set_reg(spi, M41T93_REG_ST_SEC, reset_osc);
+		}
 	}
 
 	data[M41T93_REG_SSEC]		= 0;
···
 	   1. halt bit (HT) is set: the clock is running but update of readout
 	      registers has been disabled due to power failure. This is normal
 	      case after poweron. Time is valid after resetting HT bit.
-	   2. oscillator fail bit (OF) is set. Oscillator has be stopped and
-	      time is invalid:
-	      a) OF can be immeditely reset.
-	      b) OF cannot be immediately reset: oscillator has to be restarted.
+	   2. oscillator fail bit (OF) is set: time is invalid.
 	*/
 	tmp = spi_w8r8(spi, M41T93_REG_ALM_HOUR_HT);
 	if (tmp < 0)
···
 
 	if (tmp & M41T93_FLAG_OF) {
 		ret = -EINVAL;
-		dev_warn(&spi->dev, "OF bit is set, resetting.\n");
-		m41t93_set_reg(spi, M41T93_REG_FLAGS, tmp & ~M41T93_FLAG_OF);
-
-		tmp = spi_w8r8(spi, M41T93_REG_FLAGS);
-		if (tmp < 0)
-			return tmp;
-		else if (tmp & M41T93_FLAG_OF) {
-			u8 reset_osc = buf[M41T93_REG_ST_SEC] | M41T93_FLAG_ST;
-
-			dev_warn(&spi->dev,
-				 "OF bit is still set, kickstarting clock.\n");
-			m41t93_set_reg(spi, M41T93_REG_ST_SEC, reset_osc);
-			reset_osc &= ~M41T93_FLAG_ST;
-			m41t93_set_reg(spi, M41T93_REG_ST_SEC, reset_osc);
-		}
+		dev_warn(&spi->dev, "OF bit is set, write time to restart.\n");
 	}
 
 	if (tmp & M41T93_FLAG_BL)