[PATCH AUTOSEL for 4.9 164/281] rtc: m41t80: fix SQW dividers override when setting a date

[Sasha Levin]

From: Gary Bisson <gary.bisson@xxxxxxxxxxxxxxxxxxx>

[ Upstream commit 0f546b058b86ea2f661cc7a6e931cee5a29959ef ]

This patch is only relevant for RTC with the SQ_ALT feature which
means the clock output frequency divider is stored in the weekday
register.

Current implementation discards the previous dividers value and clear
them as soon as the time is set.

Signed-off-by: Gary Bisson <gary.bisson@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Alexandre Belloni <alexandre.belloni@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx>
---
 drivers/rtc/rtc-m41t80.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/drivers/rtc/rtc-m41t80.c b/drivers/rtc/rtc-m41t80.c
index 58698d21c2c3..c4ca6a385790 100644
--- a/drivers/rtc/rtc-m41t80.c
+++ b/drivers/rtc/rtc-m41t80.c
@@ -168,6 +168,7 @@ static int m41t80_get_datetime(struct i2c_client *client,
 /* Sets the given date and time to the real time clock. */
 static int m41t80_set_datetime(struct i2c_client *client, struct rtc_time *tm)
 {
+	struct m41t80_data *clientdata = i2c_get_clientdata(client);
 	unsigned char buf[8];
 	int err, flags;
 
@@ -183,6 +184,17 @@ static int m41t80_set_datetime(struct i2c_client *client, struct rtc_time *tm)
 	buf[M41T80_REG_YEAR] = bin2bcd(tm->tm_year - 100);
 	buf[M41T80_REG_WDAY] = tm->tm_wday;
 
+	/* If the square wave output is controlled in the weekday register */
+	if (clientdata->features & M41T80_FEATURE_SQ_ALT) {
+		int val;
+
+		val = i2c_smbus_read_byte_data(client, M41T80_REG_WDAY);
+		if (val < 0)
+			return val;
+
+		buf[M41T80_REG_WDAY] |= (val & 0xf0);
+	}
+
 	err = i2c_smbus_write_i2c_block_data(client, M41T80_REG_SSEC,
 					     sizeof(buf), buf);
 	if (err < 0) {
-- 
2.14.1