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Date:   Tue, 24 Nov 2020 09:04:57 +0000
From:   Marc Zyngier <maz@kernel.org>
To:     Jianyong Wu <Jianyong.Wu@arm.com>
Cc:     netdev@vger.kernel.org, yangbo.lu@nxp.com, john.stultz@linaro.org,
        tglx@linutronix.de, pbonzini@redhat.com,
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        Mark Rutland <Mark.Rutland@arm.com>, will@kernel.org,
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        kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org,
        Steve Capper <Steve.Capper@arm.com>,
        Justin He <Justin.He@arm.com>, nd <nd@arm.com>
Subject: Re: [PATCH v15 7/9] ptp: arm/arm64: Enable ptp_kvm for arm/arm64
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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.

Thanks,

         M.
-- 
Jazz is not dead. It just smells funny...