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

From Thomas Gleixner <tglx@linutronix.de>
Newsgroups linux.kernel
Subject Re: [PATCH] clocksource/arm_global_timer: reconfigure clockevents after cpufreq change
Date 2016-11-29 14:50 +0100
Message-ID <sIQXh-F4-67@gated-at.bofh.it> (permalink)
References <sIPy9-8o8-5@gated-at.bofh.it> <sIPy9-8o8-3@gated-at.bofh.it>
Organization linux.* mail to news gateway

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On Tue, 29 Nov 2016, Alexander Kochetkov wrote:

> After a cpufreq transition, update the clockevent's frequency
> by fetching the new clock rate from the clock framework and
> reprogram the next clock event.

The frequency change would not only affect the clockevent device, it also
would affect the clocksource. So the patch is incomplete, but see below.

> The clock supplying the arm-global-timer on the rk3188 is coming
> from the the cpu clock itself and thus changes its rate everytime
> cpufreq adjusts the cpu frequency.

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.

> Found by code review, real impact not known. Assume what actual
> HZ value will be different from expected on platforms using
> arm-global-timer as clockevent.

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.

Thanks,

	tglx

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[PATCH] clocksource/arm_global_timer: reconfigure clockevents after cpufreq change Alexander Kochetkov <al.kochet@gmail.com> - 2016-11-29 13:20 +0100
  [PATCH] clocksource/arm_global_timer: reconfigure clockevents after cpufreq change Alexander Kochetkov <al.kochet@gmail.com> - 2016-11-29 13:20 +0100
    Re: [PATCH] clocksource/arm_global_timer: reconfigure clockevents  after cpufreq change Thomas Gleixner <tglx@linutronix.de> - 2016-11-29 14:50 +0100
      Re: [PATCH] clocksource/arm_global_timer: reconfigure clockevents after cpufreq change Alexander Kochetkov <al.kochet@gmail.com> - 2016-11-29 15:10 +0100
        Re: [PATCH] clocksource/arm_global_timer: reconfigure clockevents  after cpufreq change Thomas Gleixner <tglx@linutronix.de> - 2016-11-29 15:20 +0100
      Re: [PATCH] clocksource/arm_global_timer: reconfigure clockevents  after cpufreq change Marc Zyngier <marc.zyngier@arm.com> - 2016-11-29 15:20 +0100
        Re: [PATCH] clocksource/arm_global_timer: reconfigure clockevents  after cpufreq change Thomas Gleixner <tglx@linutronix.de> - 2016-11-29 15:40 +0100
          Re: [PATCH] clocksource/arm_global_timer: reconfigure clockevents after cpufreq change Alexander Kochetkov <al.kochet@gmail.com> - 2016-11-29 16:00 +0100
            Re: [PATCH] clocksource/arm_global_timer: reconfigure clockevents  after cpufreq change Robin Murphy <robin.murphy@arm.com> - 2016-11-29 16:10 +0100
          Re: [PATCH] clocksource/arm_global_timer: reconfigure clockevents  after cpufreq change Marc Zyngier <marc.zyngier@arm.com> - 2016-11-29 16:00 +0100
            Re: [PATCH] clocksource/arm_global_timer: reconfigure clockevents after cpufreq change Alexander Kochetkov <al.kochet@gmail.com> - 2016-11-29 16:10 +0100

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