linux-kernel - Re: [PATCH] timekeeping: Move persistent clock registration code from ARM to kernel

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Date:	Fri, 14 Nov 2014 01:26:44 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	John Stultz <john.stultz@...aro.org>
cc:	Anatol Pomozov <anatol.pomozov@...il.com>,
	Thierry Reding <thierry.reding@...il.com>,
	Stephen Warren <swarren@...dotorg.org>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Russell King <linux@....linux.org.uk>,
	LKML <linux-kernel@...r.kernel.org>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	Tony Lindgren <tony@...mide.com>,
	Mark Rutland <mark.rutland@....com>
Subject: Re: [PATCH] timekeeping: Move persistent clock registration code
 from ARM to kernel

On Thu, 13 Nov 2014, John Stultz wrote:
> On Thu, Nov 13, 2014 at 2:46 PM, Thomas Gleixner <tglx@...utronix.de> wrote:
> > Aside of that I really wonder why we need that persistent_clock stuff
> > at all. We already have mechanisms to register persistent clocks AKA
> > RTCs after the early boot process and update the wall clock time
> > before we actually need it. Nothing in early boot depends on correct
> > wall clock at all.
> >
> > So instead of adding more extra persistent clock nonsense, can we just
> > move all of that to the place where it belongs, i.e. RTC?
> 
> Sigh.. I've got this on an eventual todo list.. The big problem though
> is that the RTC infrastructure can't be called with irqs off, so its
> not as optimal for measuring suspend time. Some of the suspend-time
> measurement with clocksources that don't halt is interesting here.
> 
> So we need to add to the RTC infrastructure special accessors that are
> safe when irqs are off, and we can then deprecate the persistent clock
> bits. There's still evaluation quirks with setting the time earlier in
> boot or not (possibly some rng effects as well there), but that could
> be worked out if we had the suspend timing via safe RTC interfaces
> sorted.

So we better work on this instead of creating more legacy enforcement
APIs....

Thanks,

	tglx
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