linux-kernel - Re: [PATCH 1/6] arm64: dts: amlogic: Add missing cooling device properties for CPUs

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Message-ID: <9f9cc086-6069-afbc-d3c6-46608ff35b79@baylibre.com>
Date:   Sat, 26 May 2018 10:37:49 +0200
From:   Neil Armstrong <narmstrong@...libre.com>
To:     Olof Johansson <olof@...om.net>,
        Viresh Kumar <viresh.kumar@...aro.org>
Cc:     Mark Rutland <mark.rutland@....com>, devicetree@...r.kernel.org,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Will Deacon <will.deacon@....com>,
        linux-kernel@...r.kernel.org, Rob Herring <robh+dt@...nel.org>,
        arm@...nel.org, Kevin Hilman <khilman@...libre.com>,
        Carlo Caione <carlo@...one.org>, chris.redpath@....com,
        linux-amlogic@...ts.infradead.org, ionela.voinescu@....com,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 1/6] arm64: dts: amlogic: Add missing cooling device
 properties for CPUs

Hi,

On 25/05/2018 23:10, Olof Johansson wrote:
> On Fri, May 25, 2018 at 11:10:01AM +0530, Viresh Kumar wrote:
>> The cooling device properties, like "#cooling-cells" and
>> "dynamic-power-coefficient", should either be present for all the CPUs
>> of a cluster or none. If these are present only for a subset of CPUs of
>> a cluster then things will start falling apart as soon as the CPUs are
>> brought online in a different order. For example, this will happen
>> because the operating system looks for such properties in the CPU node
>> it is trying to bring up, so that it can register a cooling device.
>>
>> Add such missing properties.
> 
> This seems awkward compared to just having one cooling-cells in the /cpus node
> instead.
> 
> What's it used for? I don't see any properties in the device nodes on meson-gxm
> that have any cooling-foo cells in them? So why should #cooling-cells be
> needed?

There is no reason to have the cooling-cells on these other CPUs, the DVFS is
controlled on the first CPU of each cluster, here cpu0 and cpu4 and only
cpu0 and cpu4 are used as cooling-cells.

Neil

> 
> 
> -Olof
> 
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
> 

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