diff options
Diffstat (limited to 'drivers/rtc/class.c')
| -rw-r--r-- | drivers/rtc/class.c | 49 |
1 files changed, 49 insertions, 0 deletions
diff --git a/drivers/rtc/class.c b/drivers/rtc/class.c index 9458e6d6686a..7c88d190c51f 100644 --- a/drivers/rtc/class.c +++ b/drivers/rtc/class.c @@ -34,6 +34,50 @@ static void rtc_device_release(struct device *dev) #ifdef CONFIG_RTC_HCTOSYS_DEVICE /* Result of the last RTC to system clock attempt. */ int rtc_hctosys_ret = -ENODEV; + +/* IMPORTANT: the RTC only stores whole seconds. It is arbitrary + * whether it stores the most close value or the value with partial + * seconds truncated. However, it is important that we use it to store + * the truncated value. This is because otherwise it is necessary, + * in an rtc sync function, to read both xtime.tv_sec and + * xtime.tv_nsec. On some processors (i.e. ARM), an atomic read + * of >32bits is not possible. So storing the most close value would + * slow down the sync API. So here we have the truncated value and + * the best guess is to add 0.5s. + */ + +static void rtc_hctosys(struct rtc_device *rtc) +{ + int err; + struct rtc_time tm; + struct timespec64 tv64 = { + .tv_nsec = NSEC_PER_SEC >> 1, + }; + + err = rtc_read_time(rtc, &tm); + if (err) { + dev_err(rtc->dev.parent, + "hctosys: unable to read the hardware clock\n"); + goto err_read; + } + + tv64.tv_sec = rtc_tm_to_time64(&tm); + +#if BITS_PER_LONG == 32 + if (tv64.tv_sec > INT_MAX) { + err = -ERANGE; + goto err_read; + } +#endif + + err = do_settimeofday64(&tv64); + + dev_info(rtc->dev.parent, "setting system clock to %ptR UTC (%lld)\n", + &tm, (long long)tv64.tv_sec); + +err_read: + rtc_hctosys_ret = err; +} #endif #if defined(CONFIG_PM_SLEEP) && defined(CONFIG_RTC_HCTOSYS_DEVICE) @@ -375,6 +419,11 @@ int __rtc_register_device(struct module *owner, struct rtc_device *rtc) dev_info(rtc->dev.parent, "registered as %s\n", dev_name(&rtc->dev)); +#ifdef CONFIG_RTC_HCTOSYS_DEVICE + if (!strcmp(dev_name(&rtc->dev), CONFIG_RTC_HCTOSYS_DEVICE)) + rtc_hctosys(rtc); +#endif + return 0; } EXPORT_SYMBOL_GPL(__rtc_register_device); |