netdev - RE: [PATCH v15 7/9] ptp: arm/arm64: Enable ptp

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Message-ID: <HE1PR0802MB25557885DA7391D52353B7C5F4FB0@HE1PR0802MB2555.eurprd08.prod.outlook.com>
Date:   Tue, 24 Nov 2020 10:18:41 +0000
From:   Jianyong Wu <Jianyong.Wu@....com>
To:     Marc Zyngier <maz@...nel.org>
CC:     "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>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "sean.j.christopherson@...el.com" <sean.j.christopherson@...el.com>,
        "richardcochran@...il.com" <richardcochran@...il.com>,
        Mark Rutland <Mark.Rutland@....com>,
        "will@...nel.org" <will@...nel.org>,
        Suzuki Poulose <Suzuki.Poulose@....com>,
        Andre Przywara <Andre.Przywara@....com>,
        Steven Price <Steven.Price@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "kvmarm@...ts.cs.columbia.edu" <kvmarm@...ts.cs.columbia.edu>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        Steve Capper <Steve.Capper@....com>,
        Justin He <Justin.He@....com>, nd <nd@....com>
Subject: RE: [PATCH v15 7/9] ptp: arm/arm64: Enable ptp_kvm for arm/arm64

Hi Marc,

> -----Original Message-----
> From: Marc Zyngier <maz@...nel.org>
> Sent: Tuesday, November 24, 2020 5:05 PM
> To: Jianyong Wu <Jianyong.Wu@....com>
> Cc: netdev@...r.kernel.org; yangbo.lu@....com; john.stultz@...aro.org;
> tglx@...utronix.de; pbonzini@...hat.com; sean.j.christopherson@...el.com;
> richardcochran@...il.com; Mark Rutland <Mark.Rutland@....com>;
> will@...nel.org; Suzuki Poulose <Suzuki.Poulose@....com>; Andre
> Przywara <Andre.Przywara@....com>; Steven Price
> <Steven.Price@....com>; linux-kernel@...r.kernel.org; linux-arm-
> kernel@...ts.infradead.org; kvmarm@...ts.cs.columbia.edu;
> kvm@...r.kernel.org; Steve Capper <Steve.Capper@....com>; Justin He
> <Justin.He@....com>; nd <nd@....com>
> Subject: Re: [PATCH v15 7/9] ptp: arm/arm64: Enable ptp_kvm for
> arm/arm64
> 
> Jianyong,
> 
> On 2020-11-24 05:37, Jianyong Wu wrote:
> > Hi Marc,
> 
> [...]
> 
> >> > +
> >> 	arm_smccc_1_1_invoke(ARM_SMCCC_VENDOR_HYP_KVM_PTP_FU
> >> NC_ID,
> >> > +			     ARM_PTP_NONE_COUNTER, &hvc_res);
> >>
> >> I really don't see the need to use a non-architectural counter ID.
> >> Using the virtual counter ID should just be fine, and shouldn't lead
> >> to any issue.
> >>
> >
> >> Am I missing something?
> >
> > In this function, no counter data is needed. If virtual counter ID is
> > used here, user may be confused with why we get virtual counter
> > data and do nothing with it. So I explicitly add a new "NONE" counter
> > ID to make it clear.
> >
> > WDYT?
> 
> ITIABI (I Think It's A Bad Idea). There are two counters, and the API
> allows to retrieve the data for any of these two. If the "user" doesn't
> want to do anything with the data, that's their problem.
> 
> Here, you can just sue the virtual counter, and that will give you the
> exact same semantic, without inventing non-architectural state.
> 
OK, that's it.

Thanks
Jianyong Wu

> Thanks,
> 
>          M.
> --
> Jazz is not dead. It just smells funny...