Re: [PATCH v2 0/5] arm64: sunxi: Enable the sun4i timer

From: Daniel Lezcano <daniel.lezcano@linaro.org>
To: Samuel Holland <samuel@sholland.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Rob Herring <robh+dt@kernel.org>,
	Maxime Ripard <mripard@kernel.org>, Chen-Yu Tsai <wens@csie.org>,
	Jernej Skrabec <jernej.skrabec@siol.net>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>
Cc: devicetree@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
	linux-sunxi@lists.linux.dev, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 0/5] arm64: sunxi: Enable the sun4i timer
Date: Wed, 24 Mar 2021 10:33:06 +0100	[thread overview]
Message-ID: <0b3689ad-6bb3-bd7a-46be-0c4d3d7de268@linaro.org> (raw)
In-Reply-To: <64f6d712-11fe-4626-aa24-8e31c21a8ad4@sholland.org>

On 24/03/2021 04:51, Samuel Holland wrote:
> On 3/22/21 9:18 AM, Daniel Lezcano wrote:
>> On 22/03/2021 05:47, Samuel Holland wrote:
>>> In preparation for adding CPU idle states, hook up the sun4i timer.
>>> Having a non-c3stop clockevent source available is necessary for all
>>> CPUs to simultaneously enter a local-timer-stop idle state.
>>
>> Why simultaneously ?
> Because the CPU providing (the hrtimer providing) the broadcast timer
> cannot enter an idle state which would stop that timer. So in my case,
> with 4 CPUs, I was seeing at most 3 CPUs enter idle at any given time.
> This prevented any cluster-level idle states from doing anything. After
> applying this series, I was able to observe the whole cluster powering
> down when appropriate.

Ah, ok. I did not realize this fourth CPU was acting as the broadcast
timer, so allowing at least a CPU power down. This setup is unusual.

The changes make sense.

Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>

-- 
<http://www.linaro.org/> Linaro.org │ Open source software for ARM SoCs

Follow Linaro:  <http://www.facebook.com/pages/Linaro> Facebook |
<http://twitter.com/#!/linaroorg> Twitter |
<http://www.linaro.org/linaro-blog/> Blog