From: "A. Niyas Ahamed Mydeen" <nmydeen@xxxxxxxxxx> The ocillator on the m41t62 (and other chips of this type) needs a kickstart upon a failure; the RTC read routine will notice the oscillator failure and fail reads. This is added in the RTC write routine; this allows the system to know that the time in the RTC is accurate. This is following the procedure described in section 3.11 of "https://www.st.com/resource/en/datasheet/m41t62.pdf"; Signed-off-by: A. Niyas Ahamed Mydeen <nmydeen@xxxxxxxxxx> Reviewed-by: Corey Minyard <cminyard@xxxxxxxxxx> --- drivers/rtc/rtc-m41t80.c | 70 ++++++++++++++++++++++++++++------------ 1 file changed, 49 insertions(+), 21 deletions(-) diff --git a/drivers/rtc/rtc-m41t80.c b/drivers/rtc/rtc-m41t80.c index 1f58ae8b151e..77c21c91bae3 100644 --- a/drivers/rtc/rtc-m41t80.c +++ b/drivers/rtc/rtc-m41t80.c @@ -22,6 +22,7 @@ #include <linux/slab.h> #include <linux/mutex.h> #include <linux/string.h> +#include <linux/delay.h> #ifdef CONFIG_RTC_DRV_M41T80_WDT #include <linux/fs.h> #include <linux/ioctl.h> @@ -204,7 +205,7 @@ static int m41t80_rtc_read_time(struct device *dev, struct rtc_time *tm) return flags; if (flags & M41T80_FLAGS_OF) { - dev_err(&client->dev, "Oscillator failure, data is invalid.\n"); + dev_err(&client->dev, "Oscillator failure, time may not be accurate, write time to RTC to fix it.\n"); return -EINVAL; } @@ -227,21 +228,60 @@ static int m41t80_rtc_read_time(struct device *dev, struct rtc_time *tm) return 0; } -static int m41t80_rtc_set_time(struct device *dev, struct rtc_time *tm) +static int m41t80_rtc_set_time(struct device *dev, struct rtc_time *in_tm) { struct i2c_client *client = to_i2c_client(dev); struct m41t80_data *clientdata = i2c_get_clientdata(client); + struct rtc_time tm = *in_tm; unsigned char buf[8]; int err, flags; + time64_t time = 0; + flags = i2c_smbus_read_byte_data(client, M41T80_REG_FLAGS); + if (flags < 0) + return flags; + if (flags & M41T80_FLAGS_OF) { + /* OF cannot be immediately reset: oscillator has to be restarted. */ + dev_warn(&client->dev, "OF bit is still set, kickstarting clock.\n"); + err = i2c_smbus_write_byte_data(client, M41T80_REG_SEC, M41T80_SEC_ST); + if (err < 0) { + dev_err(&client->dev, "Can't set ST bit\n"); + return err; + } + err = i2c_smbus_write_byte_data(client, M41T80_REG_SEC, + flags & ~M41T80_SEC_ST); + if (err < 0) { + dev_err(&client->dev, "Can't clear ST bit\n"); + return err; + } + /* oscillator must run for 4sec before we attempt to reset OF bit */ + msleep(4000); + /* Clear the OF bit of Flags Register */ + err = i2c_smbus_write_byte_data(client, M41T80_REG_FLAGS, + flags & ~M41T80_FLAGS_OF); + if (err < 0) { + dev_err(&client->dev, "Unable to write flags register\n"); + return err; + } + flags = i2c_smbus_read_byte_data(client, M41T80_REG_FLAGS); + if (flags < 0) + return flags; + else if (flags & M41T80_FLAGS_OF) { + dev_err(&client->dev, "Can't clear the OF bit check battery\n"); + return err; + } + /* add 4sec of oscillator stablize time otherwise we are behind 4sec */ + time = rtc_tm_to_time64(&tm); + rtc_time64_to_tm(time+4, &tm); + } buf[M41T80_REG_SSEC] = 0; - buf[M41T80_REG_SEC] = bin2bcd(tm->tm_sec); - buf[M41T80_REG_MIN] = bin2bcd(tm->tm_min); - buf[M41T80_REG_HOUR] = bin2bcd(tm->tm_hour); - buf[M41T80_REG_DAY] = bin2bcd(tm->tm_mday); - buf[M41T80_REG_MON] = bin2bcd(tm->tm_mon + 1); - buf[M41T80_REG_YEAR] = bin2bcd(tm->tm_year - 100); - buf[M41T80_REG_WDAY] = tm->tm_wday; + buf[M41T80_REG_SEC] = bin2bcd(tm.tm_sec); + buf[M41T80_REG_MIN] = bin2bcd(tm.tm_min); + buf[M41T80_REG_HOUR] = bin2bcd(tm.tm_hour); + buf[M41T80_REG_DAY] = bin2bcd(tm.tm_mday); + buf[M41T80_REG_MON] = bin2bcd(tm.tm_mon + 1); + 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) { @@ -261,18 +301,6 @@ static int m41t80_rtc_set_time(struct device *dev, 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; - - err = i2c_smbus_write_byte_data(client, M41T80_REG_FLAGS, - flags & ~M41T80_FLAGS_OF); - if (err < 0) { - dev_err(&client->dev, "Unable to write flags register\n"); - return err; - } - return err; } -- 2.34.1
