The RZN1 RTC can compensate the imprecision of the oscillator up to
approximately 190ppm.
Seconds can last slightly shorter or longer depending on the
configuration.
Below ~65ppm of correction, we can change the time spent in a second
every minute, which is the most accurate compensation that the RTC can
offer. Above, the compensation will be active every 20s.
Signed-off-by: Miquel Raynal <miquel.raynal@xxxxxxxxxxx>
---
drivers/rtc/rtc-rzn1.c | 73 ++++++++++++++++++++++++++++++++++++++++++
1 file changed, 73 insertions(+)
diff --git a/drivers/rtc/rtc-rzn1.c b/drivers/rtc/rtc-rzn1.c
index 7ee190daa651..f340793d9fc7 100644
--- a/drivers/rtc/rtc-rzn1.c
+++ b/drivers/rtc/rtc-rzn1.c
@@ -247,12 +247,85 @@ static int rzn1_rtc_set_alarm(struct device *dev, struct rtc_wkalrm *alrm)
return 0;
}
+static int rzn1_rtc_read_offset(struct device *dev, long *offset)
+{
+ struct rzn1_rtc *rtc = dev_get_drvdata(dev);
+ unsigned int ppb_per_step;
+ bool subtract;
+ u32 val;
+
+ val = readl(rtc->base + RZN1_RTC_SUBU);
+ ppb_per_step = val & RZN1_RTC_SUBU_DEV ? 1017 : 3051;
+ subtract = val & RZN1_RTC_SUBU_DECR;
+ val &= 0x3F;
+
+ if (!val)
+ *offset = 0;
+ else if (subtract)
+ *offset = -(((~val) & 0x3F) + 1) * ppb_per_step;
+ else
+ *offset = (val - 1) * ppb_per_step;
+
+ return 0;
+}
+
+static int rzn1_rtc_set_offset(struct device *dev, long offset)
+{
+ struct rzn1_rtc *rtc = dev_get_drvdata(dev);
+ unsigned int steps;
+ int stepsh, stepsl;
+ u32 val;
+ int ret;
+
+ /*
+ * Check which resolution mode (every 20 or 60s) can be used.
+ * Between 2 and 124 clock pulses can be added or substracted.
+ *
+ * In 20s mode, the minimum resolution is 2 / (32768 * 20) which is
+ * close to 3051 ppb. In 60s mode, the resolution is closer to 1017.
+ */
+ stepsh = DIV_ROUND_CLOSEST(offset, 1017);
+ stepsl = DIV_ROUND_CLOSEST(offset, 3051);
+
+ if (stepsh >= -0x3E && stepsh <= 0x3E) {
+ /* 1017 ppb per step */
+ steps = stepsh;
+ val |= RZN1_RTC_SUBU_DEV;
+ } else if (stepsl >= -0x3E && stepsl <= 0x3E) {
+ /* 3051 ppb per step */
+ steps = stepsl;
+ } else {
+ return -ERANGE;
+ }
+
+ if (!steps)
+ return 0;
+
+ if (steps > 0) {
+ val |= steps + 1;
+ } else {
+ val |= RZN1_RTC_SUBU_DECR;
+ val |= (~(-steps - 1)) & 0x3F;
+ }
+
+ ret = readl_poll_timeout(rtc->base + RZN1_RTC_CTL2, val,
+ !(val & RZN1_RTC_CTL2_WUST), 100, 2000000);
+ if (ret)
+ return ret;
+
+ writel(val, rtc->base + RZN1_RTC_SUBU);
+
+ return 0;
+}
+
static const struct rtc_class_ops rzn1_rtc_ops = {
.read_time = rzn1_rtc_read_time,
.set_time = rzn1_rtc_set_time,
.read_alarm = rzn1_rtc_read_alarm,
.set_alarm = rzn1_rtc_set_alarm,
.alarm_irq_enable = rzn1_rtc_alarm_irq_enable,
+ .read_offset = rzn1_rtc_read_offset,
+ .set_offset = rzn1_rtc_set_offset,
};
static int rzn1_rtc_probe(struct platform_device *pdev)
--
2.27.0
