@@ -939,4 +939,61 @@ 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 the rtc offset is not setable (or not implemented), return 0 and put
+ * 0 in the offset value;
+ */
+int rtc_read_offset(struct rtc_device *rtc, long *offset)
+{
+ int ret = 0;
+
+ if (!rtc->ops)
+ return -ENODEV;
+
+ if (!rtc->ops->set_offset) {
+ offset = 0;
+ return 0;
+ }
+
+ 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 = 0;
+
+ 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;
+}
@@ -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)
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 (ppm), 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: Joshua Clayton <stillcompiling@gmail.com> --- drivers/rtc/interface.c | 57 +++++++++++++++++++++++++++++++++++++++++++++++++ include/linux/rtc.h | 4 ++++ 2 files changed, 61 insertions(+)