rtc: m41t80: handle oscillator failure bit

Handle the Oscillator Failure (OF) bit on each read of date-time.
If the OF is set, an error is returned (-EINVAL) instead of the date-time.
The OF bit is cleared each time the date is set.

Signed-off-by: Mylène Josserand <mylene.josserand@free-electrons.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>

diff --git a/drivers/rtc/rtc-m41t80.c b/drivers/rtc/rtc-m41t80.c
index 5706e99..d1bf93a 100644 (file)
--- a/drivers/rtc/rtc-m41t80.c
+++ b/drivers/rtc/rtc-m41t80.c
@@ -56,6 +56,7 @@
 #define M41T80_ALMON_AFE       BIT(7)  /* AFE: AF Enable Bit */
 #define M41T80_ALMON_SQWE      BIT(6)  /* SQWE: SQW Enable Bit */
 #define M41T80_ALHOUR_HT       BIT(6)  /* HT: Halt Update Bit */
+#define M41T80_FLAGS_OF                BIT(2)  /* OF: Oscillator Failure Bit */
 #define M41T80_FLAGS_AF                BIT(6)  /* AF: Alarm Flag Bit */
 #define M41T80_FLAGS_BATT_LOW  BIT(4)  /* BL: Battery Low Bit */
 #define M41T80_WATCHDOG_RB2    BIT(7)  /* RB: Watchdog resolution */
@@ -134,7 +135,16 @@ static int m41t80_get_datetime(struct i2c_client *client,
                               struct rtc_time *tm)
 {
        unsigned char buf[8];
-       int err;
+       int err, flags;
+
+       flags = i2c_smbus_read_byte_data(client, M41T80_REG_FLAGS);
+       if (flags < 0)
+               return flags;
+
+       if (flags & M41T80_FLAGS_OF) {
+               dev_err(&client->dev, "Oscillator failure, data is invalid.\n");
+               return -EINVAL;
+       }
 
        err = i2c_smbus_read_i2c_block_data(client, M41T80_REG_SSEC,
                                            sizeof(buf), buf);
@@ -159,7 +169,7 @@ static int m41t80_get_datetime(struct i2c_client *client,
 static int m41t80_set_datetime(struct i2c_client *client, struct rtc_time *tm)
 {
        unsigned char buf[8];
-       int err;
+       int err, flags;
 
        if (tm->tm_year < 100 || tm->tm_year > 199)
                return -EINVAL;
@@ -180,6 +190,17 @@ static int m41t80_set_datetime(struct i2c_client *client, struct rtc_time *tm)
                return err;
        }
 
+       /* Clear the OF bit of Flags Register */
+       flags = i2c_smbus_read_byte_data(client, M41T80_REG_FLAGS);
+       if (flags < 0)
+               return flags;
+
+       if (i2c_smbus_write_byte_data(client, M41T80_REG_FLAGS,
+                                     flags & ~M41T80_FLAGS_OF)) {
+               dev_err(&client->dev, "Unable to write flags register\n");
+               return -EIO;
+       }
+
        return err;
 }