The oscillator failure bit of the flags register defaults to 1 when the
m41t80 RTC device is powered up. If we don't clear it as the manual says
we should then the bit remains set permanently and since commit
05a7f27a889f ("rtc: m41t80: handle oscillator failure bit") we spam the
kernel console with an error message on every attempt to read the RTC,
for example:
Welcome to Buildroot
mips64r6-n32-le-hf-soak login: [ 15.534459] rtc-m41t80 0-0068:
Oscillator failure, data is invalid.
[ 16.526308] rtc-m41t80 0-0068: Oscillator failure, data is invalid.
[ 19.534342] rtc-m41t80 0-0068: Oscillator failure, data is invalid.
[ 20.526327] rtc-m41t80 0-0068: Oscillator failure, data is invalid.
Fix this by clearing the OF flag during probe, as the m41t80 manual
says we ought to.
Signed-off-by: Paul Burton <paul.burton@xxxxxxxxxx>
Fixes: 05a7f27a889f ("rtc: m41t80: handle oscillator failure bit")
Cc: Alessandro Zummo <a.zummo@xxxxxxxxxxxx>
Cc: Alexandre Belloni <alexandre.belloni@xxxxxxxxxxxxxxxxxx>
Cc: Mylène Josserand <mylene.josserand@xxxxxxxxxxxxxxxxxx>
Cc: rtc-linux@xxxxxxxxxxxxxxxx
Cc: <stable@xxxxxxxxxxxxxxx> # v4.7+
---
drivers/rtc/rtc-m41t80.c | 11 +++++++++++
1 file changed, 11 insertions(+)
diff --git a/drivers/rtc/rtc-m41t80.c b/drivers/rtc/rtc-m41t80.c
index 58698d21c2c3..33be6e4694f6 100644
--- a/drivers/rtc/rtc-m41t80.c
+++ b/drivers/rtc/rtc-m41t80.c
@@ -813,6 +813,17 @@ static int m41t80_probe(struct i2c_client *client,
m41t80_data->rtc = rtc;
+ /* Clear the OF (Oscillator failure) bit, which is 1 on power up */
+ rc = i2c_smbus_read_byte_data(client, M41T80_REG_FLAGS);
+ if (rc < 0) {
+ dev_warn(&client->dev, "unable to read flags");
+ } else if (rc & M41T80_FLAGS_OF) {
+ rc &= ~M41T80_FLAGS_OF;
+ rc = i2c_smbus_write_byte_data(client, M41T80_REG_FLAGS, rc);
+ if (rc)
+ dev_warn(&client->dev, "unable to clear OF flag");
+ }
+
/* Make sure HT (Halt Update) bit is cleared */
rc = i2c_smbus_read_byte_data(client, M41T80_REG_ALARM_HOUR);
--
2.12.1