On Fri, Sep 15, 2023 at 8:22 AM Guenter Roeck <linux@xxxxxxxxxxxx> wrote: > > Some userspace applications use timerfd_create() to request wakeups after > a long period of time. For example, a backup application may request a > wakeup once per week. This is perfectly fine as long as the system does > not try to suspend. However, if the system tries to suspend and the > system's RTC does not support the required alarm timeout, the suspend > operation will fail with an error such as > > rtc_cmos 00:01: Alarms can be up to one day in the future > PM: dpm_run_callback(): platform_pm_suspend+0x0/0x4a returns -22 > alarmtimer alarmtimer.4.auto: platform_pm_suspend+0x0/0x4a returned -22 after 117 usecs > PM: Device alarmtimer.4.auto failed to suspend: error -22 > > This results in a refusal to suspend the system, causing substantial > battery drain on affected systems. > > To fix the problem, use the maximum alarm time offset as reported by rtc > drivers to set the maximum alarm time. While this may result in early > wakeups from suspend, it is still much better than not suspending at all. > > This patch standardizes system behavior if the requested alarm timeout > is larger than the alarm timeout supported by the rtc chip. Currently, > in this situation, the rtc driver will do one of the following. > - It may return an error. > - It may limit the alarm timeout to the maximum supported by the rtc chip. > - It may mask the timeout by the maximum alarm timeout supported by the RTC > chip (i.e. a requested timeout of 1 day + 1 minute may result in a 1 > minute timeout). > > With this patch in place, if the rtc driver reports the maximum alarm > timeout supported by the rtc chip, the system will always limit the alarm > timeout to the maximum supported by the rtc chip. > > Cc: Brian Norris <briannorris@xxxxxxxxxxxx> > Signed-off-by: Guenter Roeck <linux@xxxxxxxxxxxx> > --- > v2: Use API function instead of accessing rtc core internals directly. > Modify comment in code per feedback received. > > kernel/time/alarmtimer.c | 11 +++++++++++ > 1 file changed, 11 insertions(+) > > diff --git a/kernel/time/alarmtimer.c b/kernel/time/alarmtimer.c > index 8d9f13d847f0..0dc68372efd0 100644 > --- a/kernel/time/alarmtimer.c > +++ b/kernel/time/alarmtimer.c > @@ -290,6 +290,17 @@ static int alarmtimer_suspend(struct device *dev) > rtc_timer_cancel(rtc, &rtctimer); > rtc_read_time(rtc, &tm); > now = rtc_tm_to_ktime(tm); > + > + /* > + * If the RTC alarm timer only supports a limited time offset, set the > + * alarm time to the maximum supported value. > + * The system may wake up earlier (possibly much earlier) than expected > + * when the alarmtimer runs. This is the best the kernel can do if > + * the alarmtimer exceeds the time that the rtc device can be programmed > + * for. > + */ > + min = rtc_bound_alarmtime(rtc, min); > + Thanks for all the iterations on this Guenter! This looks nice. Acked-by: John Stultz <jstultz@xxxxxxxxxx> thanks -john
