rtc: hym8563: Read the valid flag directly instead of caching it

The RTC has a valid bit in the seconds register that indicates whether
power was lost since the pevious time set. This bit is currently read
once at probe time, cached and updated with set_time.

Howeever, caching the bit may prevent detecting power loss at runtime
(which can happen if the RTC's supply is distinct from the the platform's).

Writing the seconds register when setting time will clear the bit,
so there should be no downside in reading the bit directly instead of
caching it.
Signed-off-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
Link: https://lore.kernel.org/r/20191212153111.966923-2-paul.kocialkowski@bootlin.comSigned-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

drivers/rtc/rtc-hym8563.c

@@ -78,7 +78,6 @@
 struct hym8563 {
 	struct i2c_client	*client;
 	struct rtc_device	*rtc;
-	bool			valid;
 #ifdef CONFIG_COMMON_CLK
 	struct clk_hw		clkout_hw;
 #endif
@@ -91,19 +90,19 @@ struct hym8563 {
 static int hym8563_rtc_read_time(struct device *dev, struct rtc_time *tm)
 {
 	struct i2c_client *client = to_i2c_client(dev);
-	struct hym8563 *hym8563 = i2c_get_clientdata(client);
 	u8 buf[7];
 	int ret;
 
-	if (!hym8563->valid) {
-		dev_warn(&client->dev, "no valid clock/calendar values available\n");
-		return -EINVAL;
-	}
-
 	ret = i2c_smbus_read_i2c_block_data(client, HYM8563_SEC, 7, buf);
 	if (ret < 0)
 		return ret;
 
+	if (buf[0] & HYM8563_SEC_VL) {
+		dev_warn(&client->dev,
+			 "no valid clock/calendar values available\n");
+		return -EINVAL;
+	}
+
 	tm->tm_sec = bcd2bin(buf[0] & HYM8563_SEC_MASK);
 	tm->tm_min = bcd2bin(buf[1] & HYM8563_MIN_MASK);
 	tm->tm_hour = bcd2bin(buf[2] & HYM8563_HOUR_MASK);
@@ -118,7 +117,6 @@ static int hym8563_rtc_read_time(struct device *dev, struct rtc_time *tm)
 static int hym8563_rtc_set_time(struct device *dev, struct rtc_time *tm)
 {
 	struct i2c_client *client = to_i2c_client(dev);
-	struct hym8563 *hym8563 = i2c_get_clientdata(client);
 	u8 buf[7];
 	int ret;
 
@@ -157,8 +155,6 @@ static int hym8563_rtc_set_time(struct device *dev, struct rtc_time *tm)
 	if (ret < 0)
 		return ret;
 
-	hym8563->valid = true;
-
 	return 0;
 }
 
@@ -556,9 +552,8 @@ static int hym8563_probe(struct i2c_client *client,
 	if (ret < 0)
 		return ret;
 
-	hym8563->valid = !(ret & HYM8563_SEC_VL);
 	dev_dbg(&client->dev, "rtc information is %s\n",
-		hym8563->valid ? "valid" : "invalid");
+		(ret & HYM8563_SEC_VL) ? "invalid" : "valid");
 
 	hym8563->rtc = devm_rtc_device_register(&client->dev, client->name,
 						&hym8563_rtc_ops, THIS_MODULE);