Re: [PATCH] rtc-m41t62: kickstart ocillator upon failure

[Corey Minyard]

Adding Alexander

On Thu, Jan 16, 2025 at 11:56:41AM +0530, nmydeen@xxxxxxxxxx wrote:
> 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";

Any comments on this?  I just saw that Alexander wasn't on the email,
not sure if they are still involved.

-corey

> 
> 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
>

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