drivers/rtc/rtc-isl12057.c: add proper handling of oscillator failure bit

As suggested by Uwe, instead of clearing oscillator failure bit
unconditionally at driver load, this patch adds proper handling of the
flag.  The driver now returns -ENODATA when reading time from the device
and oscillator failure bit is set.  The flag is now cleared only when the
a new time value is pushed to the device.

Signed-off-by: Arnaud Ebalard <arno@natisbad.org>
Reported-by: Uwe Kleine-König <uwe@kleine-koenig.org>
Acked-by: Uwe Kleine-König <uwe@kleine-koenig.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Cc: Peter Huewe <peter.huewe@infineon.com>
Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: Thierry Reding <treding@nvidia.com>
Cc: Mark Brown <broonie@kernel.org>
Cc: Grant Likely <grant.likely@linaro.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/rtc/rtc-isl12057.c

@@ -164,17 +164,32 @@ static int isl12057_rtc_read_time(struct device *dev, struct rtc_time *tm)
 {
 	struct isl12057_rtc_data *data = dev_get_drvdata(dev);
 	u8 regs[ISL12057_RTC_SEC_LEN];
+	unsigned int sr;
 	int ret;
 
 	mutex_lock(&data->lock);
+	ret = regmap_read(data->regmap, ISL12057_REG_SR, &sr);
+	if (ret) {
+		dev_err(dev, "%s: unable to read oscillator status flag\n",
+			__func__);
+		goto out;
+	} else {
+		if (sr & ISL12057_REG_SR_OSF) {
+			ret = -ENODATA;
+			goto out;
+		}
+	}
+
 	ret = regmap_bulk_read(data->regmap, ISL12057_REG_RTC_SC, regs,
 			       ISL12057_RTC_SEC_LEN);
+	if (ret)
+		dev_err(dev, "%s: unable to read RTC time\n", __func__);
+
+out:
 	mutex_unlock(&data->lock);
 
-	if (ret) {
-		dev_err(dev, "%s: RTC read failed\n", __func__);
+	if (ret)
 		return ret;
-	}
 
 	isl12057_rtc_regs_to_tm(tm, regs);
 
@@ -194,10 +209,22 @@ static int isl12057_rtc_set_time(struct device *dev, struct rtc_time *tm)
 	mutex_lock(&data->lock);
 	ret = regmap_bulk_write(data->regmap, ISL12057_REG_RTC_SC, regs,
 				ISL12057_RTC_SEC_LEN);
-	mutex_unlock(&data->lock);
+	if (ret) {
+		dev_err(dev, "%s: writing RTC time failed\n", __func__);
+		goto out;
+	}
 
-	if (ret)
-		dev_err(dev, "%s: RTC write failed\n", __func__);
+	/*
+	 * Now that RTC time has been updated, let's clear oscillator
+	 * failure flag, if needed.
+	 */
+	ret = regmap_update_bits(data->regmap, ISL12057_REG_SR,
+				 ISL12057_REG_SR_OSF, 0);
+	if (ret < 0)
+		dev_err(dev, "Unable to clear oscillator failure bit\n");
+
+out:
+	mutex_unlock(&data->lock);
 
 	return ret;
 }
@@ -219,14 +246,6 @@ static int isl12057_check_rtc_status(struct device *dev, struct regmap *regmap)
 		return ret;
 	}
 
-	/* Clear oscillator failure bit if needed */
-	ret = regmap_update_bits(regmap, ISL12057_REG_SR,
-				 ISL12057_REG_SR_OSF, 0);
-	if (ret < 0) {
-		dev_err(dev, "Unable to clear oscillator failure bit\n");
-		return ret;
-	}
-
 	/* Clear alarm bit if needed */
 	ret = regmap_update_bits(regmap, ISL12057_REG_SR,
 				 ISL12057_REG_SR_A1F, 0);