netdev - RE: [RFC PATCH v3 4/6] psci: Add hvc call service for ptp

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Message-ID: <HE1PR0801MB1676F76AE58C379A9E9006C0F4870@HE1PR0801MB1676.eurprd08.prod.outlook.com>
Date:   Wed, 25 Sep 2019 10:27:58 +0000
From:   "Jianyong Wu (Arm Technology China)" <Jianyong.Wu@....com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "yangbo.lu@....com" <yangbo.lu@....com>,
        "john.stultz@...aro.org" <john.stultz@...aro.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "sean.j.christopherson@...el.com" <sean.j.christopherson@...el.com>,
        "maz@...nel.org" <maz@...nel.org>,
        "richardcochran@...il.com" <richardcochran@...il.com>,
        Mark Rutland <Mark.Rutland@....com>,
        Will Deacon <Will.Deacon@....com>,
        Suzuki Poulose <Suzuki.Poulose@....com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        Steve Capper <Steve.Capper@....com>,
        "Kaly Xin (Arm Technology China)" <Kaly.Xin@....com>,
        "Justin He (Arm Technology China)" <Justin.He@....com>,
        nd <nd@....com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: RE: [RFC PATCH v3 4/6] psci: Add hvc call service for ptp_kvm.

Hi Paolo,

> -----Original Message-----
> From: Paolo Bonzini <pbonzini@...hat.com>
> Sent: Tuesday, September 24, 2019 10:20 PM
> To: Jianyong Wu (Arm Technology China) <Jianyong.Wu@....com>;
> netdev@...r.kernel.org; yangbo.lu@....com; john.stultz@...aro.org;
> tglx@...utronix.de; sean.j.christopherson@...el.com; maz@...nel.org;
> richardcochran@...il.com; Mark Rutland <Mark.Rutland@....com>; Will
> Deacon <Will.Deacon@....com>; Suzuki Poulose
> <Suzuki.Poulose@....com>
> Cc: linux-kernel@...r.kernel.org; kvm@...r.kernel.org; Steve Capper
> <Steve.Capper@....com>; Kaly Xin (Arm Technology China)
> <Kaly.Xin@....com>; Justin He (Arm Technology China)
> <Justin.He@....com>; nd <nd@....com>; linux-arm-
> kernel@...ts.infradead.org
> 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