Commit 1a7ed2ff authored by A. Niyas Ahamed Mydeen's avatar A. Niyas Ahamed Mydeen Committed by Alexandre Belloni
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rtc: m41t80: kickstart ocillator upon failure 

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: default avatarA. Niyas Ahamed Mydeen <nmydeen@mvista.com>
Reviewed-by: default avatarCorey Minyard <cminyard@mvista.com>
Link: https://lore.kernel.org/r/20250402120546.336657-2-nmydeen@mvista.com


Signed-off-by: default avatarAlexandre Belloni <alexandre.belloni@bootlin.com>
parent 818b6709

drivers/rtc/rtc-m41t80.c

+48 −20
Original line number Diff line number Diff line
@@ -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 +228,31 @@ 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) {

		/* 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) {
@@ -260,18 +271,35 @@ static int m41t80_rtc_set_time(struct device *dev, struct rtc_time *tm) 
		dev_err(&client->dev, "Unable to write to date registers\n");

		return err;

	}



	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 */

	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);

		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;

		}

	}



	return err;

}