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SubjectRE: [RFC PATCH v3 4/6] psci: Add hvc call service for ptp_kvm.
Hi Paolo,

> -----Original Message-----
> From: Paolo Bonzini <>
> Sent: Thursday, September 19, 2019 8:13 PM
> To: Marc Zyngier <>; Jianyong Wu (Arm Technology China)
> <>;;;
>; Mark Rutland <>; Will
> Deacon <>; Suzuki Poulose
> <>
> Cc:;; Steve Capper
> <>; Kaly Xin (Arm Technology China)
> <>; Justin He (Arm Technology China)
> <>; nd <>; linux-arm-
> Subject: Re: [RFC PATCH v3 4/6] psci: Add hvc call service for ptp_kvm.
> On 19/09/19 13:39, Marc Zyngier wrote:
> >> I don't think it's ugly but more important, using tk->tkr_mono.clock
> >> is incorrect. See how the x86 code hardcodes &kvm_clock, it's the
> >> same for ARM.
> > Not really. The guest kernel is free to use any clocksource it wishes.
> Understood, in fact it's the same on x86.
> However, for PTP to work, the cycles value returned by the clocksource must
> match the one returned by the hypercall. So for ARM
> get_device_system_crosststamp must receive the arch timer clocksource, so
> that it will return -ENODEV if the active clocksource is anything else.
As ptp_kvm clock has fixed to arm arch system counter in patch set v4, we need check if the current clocksource is system counter when return clock cycle in host,
so a helper needed to return the current clocksource.
Could I add this helper in next patch set?

Jianyong wu

> Paolo
> > In some cases, it is actually desirable (like these broken systems
> > that cannot use an in-kernel irqchip...). Maybe it is that on x86 the
> > guest only uses the kvm_clock, but that's a much harder sell on ARM.
> > The fact that ptp_kvm assumes that the clocksource is fixed doesn't
> > seem correct in that case.

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