rtc: ds1347: handle century register

The DS1347 can handle years from 0 to 9999, add century register support.

Link: https://lore.kernel.org/r/20191007134724.15505-10-alexandre.belloni@bootlin.com
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

drivers/rtc/rtc-ds1347.c

@@ -26,6 +26,7 @@
 #define DS1347_DAY_REG		0x0B
 #define DS1347_YEAR_REG		0x0D
 #define DS1347_CONTROL_REG	0x0F
+#define DS1347_CENTURY_REG	0x13
 #define DS1347_STATUS_REG	0x17
 #define DS1347_CLOCK_BURST	0x3F
 
@@ -49,9 +50,9 @@ static const struct regmap_access_table ds1347_access_table = {
 static int ds1347_read_time(struct device *dev, struct rtc_time *dt)
 {
 	struct regmap *map = dev_get_drvdata(dev);
-	unsigned int status;
-	int err;
+	unsigned int status, century, secs;
 	unsigned char buf[8];
+	int err;
 
 	err = regmap_read(map, DS1347_STATUS_REG, &status);
 	if (err)
@@ -60,9 +61,19 @@ static int ds1347_read_time(struct device *dev, struct rtc_time *dt)
 	if (status & DS1347_OSF_BIT)
 		return -EINVAL;
 
-	err = regmap_bulk_read(map, DS1347_CLOCK_BURST, buf, 8);
-	if (err)
-		return err;
+	do {
+		err = regmap_bulk_read(map, DS1347_CLOCK_BURST, buf, 8);
+		if (err)
+			return err;
+
+		err = regmap_read(map, DS1347_CENTURY_REG, &century);
+		if (err)
+			return err;
+
+		err = regmap_read(map, DS1347_SECONDS_REG, &secs);
+		if (err)
+			return err;
+	} while (buf[0] != secs);
 
 	dt->tm_sec = bcd2bin(buf[0]);
 	dt->tm_min = bcd2bin(buf[1] & 0x7f);
@@ -70,7 +81,7 @@ static int ds1347_read_time(struct device *dev, struct rtc_time *dt)
 	dt->tm_mday = bcd2bin(buf[3]);
 	dt->tm_mon = bcd2bin(buf[4]) - 1;
 	dt->tm_wday = bcd2bin(buf[5]) - 1;
-	dt->tm_year = bcd2bin(buf[6]) + 100;
+	dt->tm_year = (bcd2bin(century) * 100) + bcd2bin(buf[6]) - 1900;
 
 	return 0;
 }
@@ -78,6 +89,7 @@ static int ds1347_read_time(struct device *dev, struct rtc_time *dt)
 static int ds1347_set_time(struct device *dev, struct rtc_time *dt)
 {
 	struct regmap *map = dev_get_drvdata(dev);
+	unsigned int century;
 	unsigned char buf[8];
 	int err;
 
@@ -92,19 +104,18 @@ static int ds1347_set_time(struct device *dev, struct rtc_time *dt)
 	buf[3] = bin2bcd(dt->tm_mday);
 	buf[4] = bin2bcd(dt->tm_mon + 1);
 	buf[5] = bin2bcd(dt->tm_wday + 1);
-
-	/* year in linux is from 1900 i.e in range of 100
-	in rtc it is from 00 to 99 */
-	dt->tm_year = dt->tm_year % 100;
-
-	buf[6] = bin2bcd(dt->tm_year);
+	buf[6] = bin2bcd(dt->tm_year % 100);
 	buf[7] = bin2bcd(0x00);
 
-	/* write the rtc settings */
 	err = regmap_bulk_write(map, DS1347_CLOCK_BURST, buf, 8);
 	if (err)
 		return err;
 
+	century = (dt->tm_year / 100) + 19;
+	err = regmap_write(map, DS1347_CENTURY_REG, century);
+	if (err)
+		return err;
+
 	return regmap_update_bits(map, DS1347_STATUS_REG,
 				  DS1347_NEOSC_BIT | DS1347_OSF_BIT, 0);
 }