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um: rtc: use RTC time when calculating the alarm

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The kernel realtime and the current RTC time may have a (small) offset.
Should the kernel time be slightly in the future, then the timeout is
zero. This is problematic in time-travel mode, as a zero timeout can be
correctly configured and time never advances.

Replace the kernel realtime read with a read of the actual persistent
RTC clock. Also, for time-travel, calculate the exact nanoseconds needed
for the clock to advance.

Signed-off-by: Benjamin Berg <benjamin.berg@intel.com>
Co-developed-by: Avraham Stern <avraham.stern@intel.com>
Link: https://patch.msgid.link/20241217204906.1408011-1-benjamin@sipsolutions.net
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
This commit is contained in:
Benjamin Berg 2024-12-17 21:49:06 +01:00 committed by Johannes Berg
parent 7ee1e43a5f
commit 579e7fd383
1 changed files with 5 additions and 2 deletions
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7
arch/um/drivers/rtc_kern.c
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@ -51,6 +51,7 @@ static int uml_rtc_read_alarm(struct device *dev, struct rtc_wkalrm *alrm)
static int uml_rtc_alarm_irq_enable(struct device *dev, unsigned int enable)
{
struct timespec64 ts;
unsigned long long secs;
if (!enable && !uml_rtc_alarm_enabled)
@ -58,7 +59,8 @@ static int uml_rtc_alarm_irq_enable(struct device *dev, unsigned int enable)
uml_rtc_alarm_enabled = enable;
secs = uml_rtc_alarm_time - ktime_get_real_seconds();
read_persistent_clock64(&ts);
secs = uml_rtc_alarm_time - ts.tv_sec;
if (time_travel_mode == TT_MODE_OFF) {
if (!enable) {
@ -73,7 +75,8 @@ static int uml_rtc_alarm_irq_enable(struct device *dev, unsigned int enable)
if (enable)
time_travel_add_event_rel(&uml_rtc_alarm_event,
secs * NSEC_PER_SEC);
secs * NSEC_PER_SEC -
ts.tv_nsec);
}
return 0;