Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1532376

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

Show all headers | View raw

On 29/11/16 14:32, Thomas Gleixner wrote:
> 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?

That'd be my preferred course of action. I've located some documentation
over there [1], and page 1126 seems to indicate a profusion of
additional timers, some of which are in an always-on domain. Seems like
a much better use of someone's time...

Thanks,

	M.

[1] http://rockchip.fr/Rockchip%20RK3188%20TRM%20V1.3.pdf
-- 
Jazz is not dead. It just smells funny...

Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

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

csiph-web