Hi Rafael,
On Wed, Mar 18, 2015 at 11:30 PM, Rafael J. Wysocki <r...@rjwysocki.net> wrote:
> 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.
It's a public symbol, declared in a header file ;-)
>> 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().
The clock domain is powered on from _within_ 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).
That's an option.
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- ge...@linux-m68k.org
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
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