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Commit b3967067 authored by Joshua Clayton's avatar Joshua Clayton Committed by Alexandre Belloni
Browse files

rtc: Add functions to set and read rtc offset 



A number of rtc devices, such as the NXP pcf2123 include a facility
to adjust the clock in order to compensate for temperature or a
crystal, capacitor, etc, that results in the rtc clock not running
at exactly 32.768 kHz.

Data sheets I have seen refer to this as a clock offset, and measure it
in parts per million, however they often reference ppm to 2 digits of
precision, which makes integer ppm less than ideal.

We use parts per billion, which more than covers the precision needed
and works nicely within 32 bits

Signed-off-by: default avatarJoshua Clayton <stillcompiling@gmail.com>
Signed-off-by: default avatarAlexandre Belloni <alexandre.belloni@free-electrons.com>
parent 9d1fa4c3

drivers/rtc/interface.c

+54 −0
Original line number Diff line number Diff line
@@ -939,4 +939,58 @@ void rtc_timer_cancel(struct rtc_device *rtc, struct rtc_timer *timer) 
	mutex_unlock(&rtc->ops_lock);

}



/**

 * rtc_read_offset - Read the amount of rtc offset in parts per billion

 * @ rtc: rtc device to be used

 * @ offset: the offset in parts per billion

 *

 * see below for details.

 *

 * Kernel interface to read rtc clock offset

 * Returns 0 on success, or a negative number on error.

 * If read_offset() is not implemented for the rtc, return -EINVAL

 */

int rtc_read_offset(struct rtc_device *rtc, long *offset)

{

	int ret;



	if (!rtc->ops)

		return -ENODEV;



	if (!rtc->ops->read_offset)

		return -EINVAL;



	mutex_lock(&rtc->ops_lock);

	ret = rtc->ops->read_offset(rtc->dev.parent, offset);

	mutex_unlock(&rtc->ops_lock);

	return ret;

}



/**

 * rtc_set_offset - Adjusts the duration of the average second

 * @ rtc: rtc device to be used

 * @ offset: the offset in parts per billion

 *

 * Some rtc's allow an adjustment to the average duration of a second

 * to compensate for differences in the actual clock rate due to temperature,

 * the crystal, capacitor, etc.

 *

 * Kernel interface to adjust an rtc clock offset.

 * Return 0 on success, or a negative number on error.

 * If the rtc offset is not setable (or not implemented), return -EINVAL

 */

int rtc_set_offset(struct rtc_device *rtc, long offset)

{

	int ret;



	if (!rtc->ops)

		return -ENODEV;



	if (!rtc->ops->set_offset)

		return -EINVAL;



	mutex_lock(&rtc->ops_lock);

	ret = rtc->ops->set_offset(rtc->dev.parent, offset);

	mutex_unlock(&rtc->ops_lock);

	return ret;

}

include/linux/rtc.h

+4 −0
Original line number Diff line number Diff line
@@ -89,6 +89,8 @@ struct rtc_class_ops { 
	int (*set_mmss)(struct device *, unsigned long secs);

	int (*read_callback)(struct device *, int data);

	int (*alarm_irq_enable)(struct device *, unsigned int enabled);

	int (*read_offset)(struct device *, long *offset);

	int (*set_offset)(struct device *, long offset);

};



#define RTC_DEVICE_NAME_SIZE 20
@@ -208,6 +210,8 @@ void rtc_timer_init(struct rtc_timer *timer, void (*f)(void *p), void *data); 
int rtc_timer_start(struct rtc_device *rtc, struct rtc_timer *timer,

		    ktime_t expires, ktime_t period);

void rtc_timer_cancel(struct rtc_device *rtc, struct rtc_timer *timer);

int rtc_read_offset(struct rtc_device *rtc, long *offset);

int rtc_set_offset(struct rtc_device *rtc, long offset);

void rtc_timer_do_work(struct work_struct *work);



static inline bool is_leap_year(unsigned int year)