linux-kernel - Re: [PATCH] clocksource/arm_global_timer: reconfigure clockevents after cpufreq change

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Date:   Tue, 29 Nov 2016 15:09:46 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Alexander Kochetkov <al.kochet@...il.com>
cc:     LKML <linux-kernel@...r.kernel.org>,
        LAK <linux-arm-kernel@...ts.infradead.org>, kernel@...inux.com,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Patrice Chotard <patrice.chotard@...com>,
        Marc Zyngier <marc.zyngier@....com>,
        Mark Rutland <mark.rutland@....com>
Subject: Re: [PATCH] clocksource/arm_global_timer: reconfigure clockevents
 after cpufreq change

On Tue, 29 Nov 2016, Alexander Kochetkov wrote:
> > 29 нояб. 2016 г., в 16:42, Thomas Gleixner <tglx@...utronix.de> написал(а):
> > 
> > The frequency change would not only affect the clockevent device, it also
> > would affect the clocksource. So the patch is incomplete, but see below.
> Looks like kernel disallow change clocksource and shed_clock rate at
> runtime. I haven’t found any function for that.
> 
> > 29 нояб. 2016 г., в 16:42, Thomas Gleixner <tglx@...utronix.de> написал(а):
> > 
> > That's broken and the clk framework should keep the CORE_PERI clock at a
> > constant rate by reprogramming the divider of the CPU clock.
> 
> Thank you for the hint.
> 
> > Assumptions w/o real impact are a perfect reason not to apply that
> > patch. This want's a proper proof that the global timer really changes and
> > this hackery is required, which I seriously doubt.
> 
> It really changes. It changes like it changes for smp-twd. I guess they are
> driven by same clock CORE_PERI.

If that happens then the whole thing wants to be disabled on those
misconfigured systems and not just hacked for nothing.

Thanks,

	tglx