On Wednesday, March 18, 2015 05:25:46 PM Geert Uytterhoeven wrote:
> The PM Domain code uses ktime_get() to perform various latency
> measurements. However, if ktime_get() is called while timekeeping is
> suspended, the following warning is printed:
>
> WARNING: CPU: 0 PID: 1340 at kernel/time/timekeeping.c:576
> ktime_get+0x30/0xf4()
>
> This happens when resuming the PM Domain that contains the clock events
> source. Chain of operations is:
>
> timekeeping_resume()
> {
> clockevents_resume()
> sh_cmt_clock_event_resume()
> pm_genpd_syscore_poweron()
> pm_genpd_sync_poweron()
> genpd_power_on()
> ktime_get(), but timekeeping_suspended == 1
> ...
> timekeeping_suspended = 0;
> }
>
> Skip all latency measurements if timekeeping is suspended to fix this.
I don't think that this is where we should fix it. At least using
timekeeping_suspended outside of the timekeeping core would not be
welcome by its maintainers.
> Signed-off-by: Geert Uytterhoeven <geert+rene...@glider.be>
> ---
> I'm not sure if this is needed for all latency measurements.
> So far I only encountered it while powering-on a clock domain during
> resume from s2ram.
The problem seems to be that the clock domain is powered on in a
syscore resume routine which happens to be called before timekeeping_resume().
It looks like we either need to force the right ordering somehow or have a
special variant of GENPD_DEV_TIMED_CALLBACK() for syscore suspend/resume that
won't do the latency measurement at all (which doesn't make much sense at
this point, because time is effectively "frozen" then).
Rafael
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