linux-kernel - Re: [PATCH] ARM: twd: Adjust localtimer frequency withcpufreqnotifiers

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Date:	Mon, 16 May 2011 18:33:11 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Colin Cross <ccross@...roid.com>
cc:	Santosh Shilimkar <santosh.shilimkar@...com>,
	Russell King <linux@....linux.org.uk>,
	Srinidhi KASAGAR <srinidhi.kasagar@...ricsson.com>,
	Harald Gustafsson <harald.gustafsson@...csson.com>,
	Linus Walleij <linus.ml.walleij@...il.com>,
	Linus Walleij <linus.walleij@...aro.org>,
	linux-kernel@...r.kernel.org,
	Rickard ANDERSSON <rickard.andersson@...ricsson.com>,
	Varun Swara <Varun.Swara@....com>,
	martin persson <martin.persson@...ricsson.com>,
	Catalin Marinas <catalin.marinas@....com>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] ARM: twd: Adjust localtimer frequency
 withcpufreqnotifiers

On Mon, 16 May 2011, Colin Cross wrote:
> On Mon, May 16, 2011 at 7:44 AM, Thomas Gleixner <tglx@...utronix.de> wrote:
> > On Mon, 16 May 2011, Santosh Shilimkar wrote:
> >> On 5/14/2011 9:21 PM, Thomas Gleixner wrote:
> >> Just for my understanding, the clockevents_reconfigure() needs to
> >> be called with interrupts disabled on that CPU as part of
> >> the CPUFREQ notifiers. I assume the right place is do it
> >> in POST notifier after the CPU clock and hence TWD clock is
> >> updated. Is that right ?
> >
> > Yes.
> 
> Is it safe to only call it in POST?  If the frequency is increasing,
> and the TWD is not updated until after the CPU frequency has changed,
> it is possible for a clockevent to fire too early.  Will that cause
> problems, or does the clockevent code check against a clocksource to
> ensure the desired time has been reached?  If that is OK, it
> drastically simplifies the code, because the driver only needs to know
> the current TWD frequency, not predict a future TWD frequency.

Yes, the hrtimer code checks against current time, so if it fires too
early it rearms the timer.
 
Thanks,

	tglx
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