Re: [RFC/PATCH 00/11] arm: omap: counter32k rework

[Tony Lindgren <tony-4v6yS6AI5VpBDgjK7y7TUQ@public.gmane.org>]

* Arnd Bergmann <arnd-r2nGTMty4D4@public.gmane.org> [151005 04:08]:
> On Monday 05 October 2015 03:55:55 Tony Lindgren wrote:
> > * Daniel Lezcano <daniel.lezcano-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org> [151001 15:16]:
> > > On 09/30/2015 04:49 PM, Arnd Bergmann wrote:
> > > >On Wednesday 30 September 2015 16:42:21 Arnd Bergmann wrote:
> > > >>
> > > >>TEGRA folks: the tegra_read_persistent_clock() implementation apparently
> > > >>predates the Tegra RTC driver and I wonder if they actually do the
> > > >>right thing in combination. Could it be that the wall time forwards
> > > >>twice as fast as it should during resume when the RTC driver is loaded?
> > > >>Could it be that we can simply remove  tegra_read_persistent_clock()
> > > >>and the register_persistent_clock() infrastructure?
> > > >>
> > > >
> > > >I found the 'sleeptime_injected' variable now, which takes care of
> > > >forwarding the clock by the correct amount.
> > > >
> > > >I also found the CLOCK_SOURCE_SUSPEND_NONSTOP flag next to it, which
> > > >should let us use the counter32k driver to provide the correct
> > > >time during suspend without the omap_read_persistent_clock() function.
> > > >We should be able to just delete that code.
> > > >
> > > >If we decide to also delete the tegra_read_persistent_clock()
> > > >function, we can remove the registration too.
> > > 
> > > 
> > > +1
> > 
> > We could maybe have read_persistent_clock() just check for the
> > CLOCK_SOURCE_SUSPEND_NONSTOP flag?
> 
> timekeeping_resume() already ignores the persistent clock values if
> the clocksource has this set. Do you mean we should additionally
> not call the read_persistent_clock() function at all to safe a
> few cycles reading that value?

Hmm no I mean if we have CLOCK_SOURCE_SUSPEND_NONSTOP we can
automatically make read_persistent_clock() use that if nothing
else got registered.

> How expensive is the function?

Usually the persistent clock is on some interconnect, so it is
way slower compared to a local timer. It doubt it makes a
difference in timekeeping_resume() though :)

Regards,

Tony