RE: [RFC PATCH v3 4/6] psci: Add hvc call service for ptp_kvm.

[Jianyong Wu (Arm Technology China)]

Hi Paolo,

> -----Original Message-----
> From: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> Sent: Tuesday, September 24, 2019 10:20 PM
> To: Jianyong Wu (Arm Technology China) <Jianyong.Wu@xxxxxxx>;
> netdev@xxxxxxxxxxxxxxx; yangbo.lu@xxxxxxx; john.stultz@xxxxxxxxxx;
> tglx@xxxxxxxxxxxxx; sean.j.christopherson@xxxxxxxxx; maz@xxxxxxxxxx;
> richardcochran@xxxxxxxxx; Mark Rutland <Mark.Rutland@xxxxxxx>; Will
> Deacon <Will.Deacon@xxxxxxx>; Suzuki Poulose
> <Suzuki.Poulose@xxxxxxx>
> Cc: linux-kernel@xxxxxxxxxxxxxxx; kvm@xxxxxxxxxxxxxxx; Steve Capper
> <Steve.Capper@xxxxxxx>; Kaly Xin (Arm Technology China)
> <Kaly.Xin@xxxxxxx>; Justin He (Arm Technology China)
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> kernel@xxxxxxxxxxxxxxxxxxx
> Subject: Re: [RFC PATCH v3 4/6] psci: Add hvc call service for ptp_kvm.
> 
> On 23/09/19 06:57, Jianyong Wu (Arm Technology China) wrote:
> >> On 19/09/19 11:46, Jianyong Wu (Arm Technology China) wrote:
> >>>> On 18/09/19 11:57, Jianyong Wu (Arm Technology China) wrote:
> >>>>> Paolo Bonzini wrote:
> >>>>>> This is not Y2038-safe.  Please use ktime_get_real_ts64 instead,
> >>>>>> and split the 64-bit seconds value between val[0] and val[1].
> >>>
> >>> Val[] should be long not u32 I think, so in arm64 I can avoid that
> >>> Y2038_safe, but also need rewrite for arm32.
> >>
> >> I don't think there's anything inherently wrong with u32 val[], and
> >> as you notice it lets you reuse code between arm and arm64.  It's up
> >> to you and Marc to decide.
> >>
> > To compatible 32-bit, Integrates second value and nanosecond value as
> > a nanosecond value then split it into val[0] and val[1] and split cycle value
> into val[2] and val[3],  In this way, time will overflow at Y2262.
> > WDYT?
> 
> So if I understand correctly you'd multiply by 10^9 (or better shift by
> 30) the nanoseconds.
> 
Yeah, 
> That works, but why not provide 5 output registers?  Alternatively, take an
> address as input and write there.

It will be easy,  if I could have expanded the store room. But these code is the infrastructure for hypercall, I can't change them at my will.
I think only value but pointer can delivered by smccc_set_retval call.

> 
> Finally, on x86 we added an argument for the CLOCK_* that is being read
> (currently only CLOCK_REALTIME, but having room for extensibility in the API
> is always nice).
> 
IMO, I will be limited by the design of hypercall on arm64, I can only design my code under it. maybe it will be better sometime but for now I could just obey it.

Thanks
Jianyong  Wu

> Paolo