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rtc: rzn1: Add oscillator offset support

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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@bootlin.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20220516082504.33913-5-miquel.raynal@bootlin.com
This commit is contained in:
Miquel Raynal 2022-05-16 10:25:03 +02:00 committed by Alexandre Belloni
parent b5ad1bf00d
commit be4a11cf98
1 changed files with 73 additions and 0 deletions
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73
drivers/rtc/rtc-rzn1.c
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@ -245,12 +245,85 @@ 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)