Re: [PATCH RESEND] alarmtimer: Use aie_timer from RTC device instead of own timer

[Mario Limonciello]

On 10/1/2024 03:30, Thomas Gleixner wrote:
> On Mon, Sep 30 2024 at 13:29, Mario Limonciello wrote:
> > It was reported that suspend-then-hibernate stopped working with modern
> > systemd versions on an AMD Cezanne system. The reason for this breakage
> > was because systemd switched to using alarmtimer instead of the wakealarm
> > sysfs file.
> >
> > The wakealarm sysfs file programs the time to the `rtc->aie_timer` member
> > of the RTC, whereas the alarmtimer suspend routine programs it to it's
> > own device.
> >
> > On AMD Cezanne systems rtc_read_alarm() is used to program a secondary
> > timer with the value of the timer. This behavior was introduced by
> > commit 59348401ebed9 ("platform/x86: amd-pmc: Add special handling
> > for timer based S0i3 wakeup").
> >
> > As rtc_read_alarm() uses the `rtc->aie_timer` to report the cached
> > timer no alarm is provided as enabled.
> >
> > To fix this issue, drop the use of a dedicated timer for the alarmtimer
> > and instead use `rtc->aie_timer` in the alarmtimer suspend/resume
> > routines.
>
> I'm not sure that this is correct. There is a reason why alarmtimer uses
> a dedicated timer 

Do you know what it is?  When I was looking at this problem I wasn't sure.

> and this worked correctly so far.
>
> I'd rather look at commit 59348401ebed9, which plays games with the RTC.
>
> Thanks,
>
>          tglx

The workaround in commit 59348401ebed9 exists because of what appears to 
be a platform bug that is unique to Cezanne systems.  Newer stuff 
(Mendocino, Rembrandt, Phoenix, Strix etc) doesn't need or use it.

I'd love if we could tear it out; but I'm at a loss what else we can do 
from the Linux kernel side.