Hi Paolo, > -----Original Message----- > From: Paolo Bonzini <[email protected]> > Sent: Thursday, September 19, 2019 8:13 PM > To: Marc Zyngier <[email protected]>; Jianyong Wu (Arm Technology China) > <[email protected]>; [email protected]; [email protected]; > [email protected]; [email protected]; [email protected]; > [email protected]; Mark Rutland <[email protected]>; Will > Deacon <[email protected]>; Suzuki Poulose > <[email protected]> > Cc: [email protected]; [email protected]; Steve Capper > <[email protected]>; Kaly Xin (Arm Technology China) > <[email protected]>; Justin He (Arm Technology China) > <[email protected]>; nd <[email protected]>; linux-arm- > [email protected] > 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?
Thanks 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.
