lkml.org 
[lkml]   [2019]   [Oct]   [9]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRE: [RFC PATCH v3 4/6] psci: Add hvc call service for ptp_kvm.
Date
Hi Paolo,

> -----Original Message-----
> From: Paolo Bonzini <pbonzini@redhat.com>
> Sent: Thursday, September 19, 2019 8:13 PM
> To: Marc Zyngier <maz@kernel.org>; Jianyong Wu (Arm Technology China)
> <Jianyong.Wu@arm.com>; netdev@vger.kernel.org; yangbo.lu@nxp.com;
> john.stultz@linaro.org; tglx@linutronix.de; sean.j.christopherson@intel.com;
> richardcochran@gmail.com; Mark Rutland <Mark.Rutland@arm.com>; Will
> Deacon <Will.Deacon@arm.com>; Suzuki Poulose
> <Suzuki.Poulose@arm.com>
> Cc: linux-kernel@vger.kernel.org; kvm@vger.kernel.org; Steve Capper
> <Steve.Capper@arm.com>; Kaly Xin (Arm Technology China)
> <Kaly.Xin@arm.com>; Justin He (Arm Technology China)
> <Justin.He@arm.com>; nd <nd@arm.com>; linux-arm-
> kernel@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.

\
 
 \ /
  Last update: 2019-10-09 07:22    [W:0.436 / U:0.700 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site