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Date: Tue, 29 Nov 2016 14:51:31 +0000 From: Marc Zyngier <marc.zyngier@....com> To: Thomas Gleixner <tglx@...utronix.de> Cc: Alexander Kochetkov <al.kochet@...il.com>, 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>, Mark Rutland <mark.rutland@....com> Subject: Re: [PATCH] clocksource/arm_global_timer: reconfigure clockevents after cpufreq change 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...
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