rtc: rv3029: correctly handle PON and VLOW2

In case the data is invalid (PON or VLOW2 are set in STATUS, explicitly
tell userspace that the time is invalid. Only remove VLOW2 when setting a
new valid time.

Link: https://lore.kernel.org/r/20191214221022.622482-12-alexandre.belloni@bootlin.comSigned-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

drivers/rtc/rtc-rv3029c2.c

@@ -159,20 +159,21 @@ static int rv3029_eeprom_enter(struct rv3029_data *rv3029)
 	ret = regmap_read(rv3029->regmap, RV3029_STATUS, &sr);
 	if (ret < 0)
 		return ret;
-	if (sr & (RV3029_STATUS_VLOW1 | RV3029_STATUS_VLOW2)) {
+	if (sr & RV3029_STATUS_VLOW2)
+		return -ENODEV;
+	if (sr & RV3029_STATUS_VLOW1) {
 		/* We clear the bits and retry once just in case
 		 * we had a brown out in early startup.
 		 */
 		ret = regmap_update_bits(rv3029->regmap, RV3029_STATUS,
-					 RV3029_STATUS_VLOW1 |
-					 RV3029_STATUS_VLOW2, 0);
+					 RV3029_STATUS_VLOW1, 0);
 		if (ret < 0)
 			return ret;
 		usleep_range(1000, 10000);
 		ret = regmap_read(rv3029->regmap, RV3029_STATUS, &sr);
 		if (ret < 0)
 			return ret;
-		if (sr & (RV3029_STATUS_VLOW1 | RV3029_STATUS_VLOW2)) {
+		if (sr & RV3029_STATUS_VLOW1) {
 			dev_err(rv3029->dev,
 				"Supply voltage is too low to safely access the EEPROM.\n");
 			return -ENODEV;
@@ -306,9 +307,17 @@ static irqreturn_t rv3029_handle_irq(int irq, void *dev_id)
 static int rv3029_read_time(struct device *dev, struct rtc_time *tm)
 {
 	struct rv3029_data *rv3029 = dev_get_drvdata(dev);
+	unsigned int sr;
 	int ret;
 	u8 regs[RV3029_WATCH_SECTION_LEN] = { 0, };
 
+	ret = regmap_read(rv3029->regmap, RV3029_STATUS, &sr);
+	if (ret < 0)
+		return ret;
+
+	if (sr & (RV3029_STATUS_VLOW2 | RV3029_STATUS_PON))
+		return -EINVAL;
+
 	ret = regmap_bulk_read(rv3029->regmap, RV3029_W_SEC, regs,
 			       RV3029_WATCH_SECTION_LEN);
 	if (ret < 0) {
@@ -454,9 +463,9 @@ static int rv3029_set_time(struct device *dev, struct rtc_time *tm)
 	if (ret < 0)
 		return ret;
 
-	/* clear PON bit */
+	/* clear PON and VLOW2 bits */
 	return regmap_update_bits(rv3029->regmap, RV3029_STATUS,
-				  RV3029_STATUS_PON, 0);
+				  RV3029_STATUS_PON | RV3029_STATUS_VLOW2, 0);
 }
 
 static int rv3029_ioctl(struct device *dev, unsigned int cmd, unsigned long arg)