linux-kernel - Re: [PATCH v3 2/2] clocksource: arm_arch_timer: Correct fault programming of CNTKCTL

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Date:   Sat, 5 Dec 2020 19:30:20 +0100
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Marc Zyngier <maz@...nel.org>
Cc:     Keqian Zhu <zhukeqian1@...wei.com>, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        kvm@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        James Morse <james.morse@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Julien Thierry <julien.thierry.kdev@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alexios Zavras <alexios.zavras@...el.com>,
        wanghaibin.wang@...wei.com
Subject: Re: [PATCH v3 2/2] clocksource: arm_arch_timer: Correct fault
 programming of CNTKCTL_EL1.EVNTI


Hi Marc,

On 05/12/2020 19:22, Marc Zyngier wrote:
> Hi Daniel,
> 
> On 2020-12-05 11:15, Daniel Lezcano wrote:
>> Hi Marc,
>>
>> are you fine with this patch ?
> 
> I am, although there still isn't any justification for the pos/lsb
> rework in the commit message (and calling that variable lsb is somewhat
> confusing). If you are going to apply it, please consider adding
> the additional comment below.

Ok, I will do that.

Thanks for the additional comment

  -- Daniel


>> On 04/12/2020 08:31, Keqian Zhu wrote:
>>> ARM virtual counter supports event stream, it can only trigger an event
>>> when the trigger bit (the value of CNTKCTL_EL1.EVNTI) of CNTVCT_EL0
>>> changes,
>>> so the actual period of event stream is 2^(cntkctl_evnti + 1). For
>>> example,
>>> when the trigger bit is 0, then virtual counter trigger an event for
>>> every
>>> two cycles.
> 
> "While we're at it, rework the way we compute the trigger bit position by
>  making it more obvious that when bits [n:n-1] are both set (with n being
>  the most significant bit), we pick bit (n + 1)."
> 
> With that:
> 
> Acked-by: Marc Zyngier <maz@...nel.org>
> 
> Thanks,
> 
>         M.


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