Re: [PATCH v3 2/2] clocksource: arm_arch_timer: Correct fault programming of CNTKCTL_EL1.EVNTI

From: Marc Zyngier <maz@kernel.org>
To: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: Keqian Zhu <zhukeqian1@huawei.com>,
	linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org,
	Thomas Gleixner <tglx@linutronix.de>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>, James Morse <james.morse@arm.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	Sean Christopherson <sean.j.christopherson@intel.com>,
	Julien Thierry <julien.thierry.kdev@gmail.com>,
	Mark Brown <broonie@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Alexios Zavras <alexios.zavras@intel.com>,
	wanghaibin.wang@huawei.com
Subject: Re: [PATCH v3 2/2] clocksource: arm_arch_timer: Correct fault programming of CNTKCTL_EL1.EVNTI
Date: Sat, 05 Dec 2020 18:22:04 +0000	[thread overview]
Message-ID: <ef43679b6710fc4320203975bc2bde98@kernel.org> (raw)
In-Reply-To: <a82cf9ff-f18d-ce0a-f7a2-82a56cbbec40@linaro.org>

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.

> 
> 
> 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@kernel.org>

Thanks,

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