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 15:40 +0100
Message-ID	<sIRJE-1es-35@gated-at.bofh.it> (permalink)
References	<sIPy9-8o8-5@gated-at.bofh.it> <sIPy9-8o8-3@gated-at.bofh.it> <sIQXh-F4-67@gated-at.bofh.it> <sIRqh-17H-21@gated-at.bofh.it>
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On Tue, 29 Nov 2016, Marc Zyngier wrote:
> On 29/11/16 13:42, Thomas Gleixner wrote:
> > 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.
> 
> Well, let's not underestimate the "creativity" [1] of A5/A9 when it
> comes to the timer clocks, and it is a very sad fact that both the
> global timer and the local timers are clocked by PERIPHCLK, which is
> ticking at a fixed ratio N (N >= 2) of the main CPU clock (CLK):
> 
> http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.ddi0407f/CIHGECHJ.html
> 
> I'm not sure how feasible it is to change this ratio (the TRM seems to
> be very silent on the subject).

The CRU documentation of the RK3188 suggests that you can adjust it as it
has a seperate divider, but who knows.

> So short of being able to reconfigure it on the fly, this will probably
> need some surgery similar to what we already do for the TWD (which this
> patch mimics).
>
> Thankfully, we don't see that anymore on moderately recent HW (anything
> since A15) and the advent of the arch timer, which is guaranteed to have
> a fixed frequency.

Can we just disable that global timer on affected SoCs and use something
else instead?

Thanks,

	tglx

Thread

[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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