diff options
author | Miquel Raynal <miquel.raynal@bootlin.com> | 2022-05-16 11:25:03 +0300 |
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committer | Alexandre Belloni <alexandre.belloni@bootlin.com> | 2022-05-18 00:11:44 +0300 |
commit | be4a11cf98aff5d456eae947a49b6163393d9420 (patch) | |
tree | fbe0e559a2b2f97d9ecba00a1897ce502d4594fe /drivers/rtc/rtc-rzn1.c | |
parent | b5ad1bf00d2c4bf96bf9318f44a929f0b22dd29c (diff) | |
download | linux-be4a11cf98aff5d456eae947a49b6163393d9420.tar.xz |
rtc: rzn1: Add oscillator offset support
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
Diffstat (limited to 'drivers/rtc/rtc-rzn1.c')
-rw-r--r-- | drivers/rtc/rtc-rzn1.c | 73 |
1 files changed, 73 insertions, 0 deletions
diff --git a/drivers/rtc/rtc-rzn1.c b/drivers/rtc/rtc-rzn1.c index c1b082e3c8a7..980ade8c9601 100644 --- a/drivers/rtc/rtc-rzn1.c +++ b/drivers/rtc/rtc-rzn1.c @@ -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) |