drivers/rtc/rtc-rx8581.c: fix setdatetime

Fix the logic while writing new date/time to the chip.  The driver
incorrectly wrote back register values to different registers and even
with wrong mask.  The patch adds clearing of the VLF register, which
should be cleared if all date/time values are set.
Signed-off-by: Rudolf Marek <rudolf.marek@sysgo.com>
Acked-by: Wan ZongShun <mcuos.com@gmail.com>
Cc: Martyn Welch <martyn.welch@gefanuc.com>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/rtc/rtc-rx8581.c

@@ -168,7 +168,7 @@ static int rx8581_set_datetime(struct i2c_client *client, struct rtc_time *tm)
 		return -EIO;
 	}
 
-	err = i2c_smbus_write_byte_data(client, RX8581_REG_FLAG,
+	err = i2c_smbus_write_byte_data(client, RX8581_REG_CTRL,
 		(data | RX8581_CTRL_STOP));
 	if (err < 0) {
 		dev_err(&client->dev, "Unable to write control register\n");
@@ -182,6 +182,20 @@ static int rx8581_set_datetime(struct i2c_client *client, struct rtc_time *tm)
 		return -EIO;
 	}
 
+	/* get VLF and clear it */
+	data = i2c_smbus_read_byte_data(client, RX8581_REG_FLAG);
+	if (data < 0) {
+		dev_err(&client->dev, "Unable to read flag register\n");
+		return -EIO;
+	}
+
+	err = i2c_smbus_write_byte_data(client, RX8581_REG_FLAG,
+		(data & ~(RX8581_FLAG_VLF)));
+	if (err != 0) {
+		dev_err(&client->dev, "Unable to write flag register\n");
+		return -EIO;
+	}
+
 	/* Restart the clock */
 	data = i2c_smbus_read_byte_data(client, RX8581_REG_CTRL);
 	if (data < 0) {
@@ -189,8 +203,8 @@ static int rx8581_set_datetime(struct i2c_client *client, struct rtc_time *tm)
 		return -EIO;
 	}
 
-	err = i2c_smbus_write_byte_data(client, RX8581_REG_FLAG,
-		(data | ~(RX8581_CTRL_STOP)));
+	err = i2c_smbus_write_byte_data(client, RX8581_REG_CTRL,
+		(data & ~(RX8581_CTRL_STOP)));
 	if (err != 0) {
 		dev_err(&client->dev, "Unable to write control register\n");
 		return -EIO;