Hi Paolo, > -----Original Message----- > From: Paolo Bonzini <pbonz...@redhat.com> > Sent: Thursday, September 19, 2019 8:13 PM > To: Marc Zyngier <m...@kernel.org>; Jianyong Wu (Arm Technology China) > <jianyong...@arm.com>; net...@vger.kernel.org; yangbo...@nxp.com; > john.stu...@linaro.org; t...@linutronix.de; sean.j.christopher...@intel.com; > richardcoch...@gmail.com; Mark Rutland <mark.rutl...@arm.com>; Will > Deacon <will.dea...@arm.com>; Suzuki Poulose > <suzuki.poul...@arm.com> > Cc: linux-kernel@vger.kernel.org; k...@vger.kernel.org; Steve Capper > <steve.cap...@arm.com>; Kaly Xin (Arm Technology China) > <kaly....@arm.com>; Justin He (Arm Technology China) > <justin...@arm.com>; nd <n...@arm.com>; linux-arm- > ker...@lists.infradead.org > 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.
