RE: [PATCH v15 7/9] ptp: arm/arm64: Enable ptp_kvm for arm/arm64

[Jianyong Wu]

Hi Marc,

> -----Original Message-----
> From: Marc Zyngier <maz@xxxxxxxxxx>
> Sent: Tuesday, November 24, 2020 5:05 PM
> To: Jianyong Wu <Jianyong.Wu@xxxxxxx>
> Cc: netdev@xxxxxxxxxxxxxxx; yangbo.lu@xxxxxxx; john.stultz@xxxxxxxxxx;
> tglx@xxxxxxxxxxxxx; pbonzini@xxxxxxxxxx; sean.j.christopherson@xxxxxxxxx;
> richardcochran@xxxxxxxxx; Mark Rutland <Mark.Rutland@xxxxxxx>;
> will@xxxxxxxxxx; Suzuki Poulose <Suzuki.Poulose@xxxxxxx>; Andre
> Przywara <Andre.Przywara@xxxxxxx>; Steven Price
> <Steven.Price@xxxxxxx>; linux-kernel@xxxxxxxxxxxxxxx; linux-arm-
> kernel@xxxxxxxxxxxxxxxxxxx; kvmarm@xxxxxxxxxxxxxxxxxxxxx;
> kvm@xxxxxxxxxxxxxxx; Steve Capper <Steve.Capper@xxxxxxx>; Justin He
> <Justin.He@xxxxxxx>; nd <nd@xxxxxxx>
> 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...