linux-kernel - Re: [PATCH 07/15] arm: dts: exynos: Add missing cooling device properties for CPUs

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Date:   Wed, 30 May 2018 14:32:12 +0200
From:   Krzysztof Kozlowski <krzk@...nel.org>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     arm@...nel.org, Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Kukjin Kim <kgene@...nel.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        ionela.voinescu@....com,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        chris.redpath@....com, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        "linux-samsung-soc@...r.kernel.org" 
        <linux-samsung-soc@...r.kernel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 07/15] arm: dts: exynos: Add missing cooling device
 properties for CPUs

On Wed, May 30, 2018 at 6:38 AM, Viresh Kumar <viresh.kumar@...aro.org> wrote:
> On 29-05-18, 15:18, Krzysztof Kozlowski wrote:
>> Thanks for the patch.
>>
>> In case of Exynos, the booting CPU always has these information in DT
>> and the booting CPU cannot be changed (chosen by firmware/hardware
>> configuration).
>
> But can the booting CPU be offlined ?
>
> If yes, then this is how things are broken right now.
>
> Build cpufreq driver as module, boot kernel, hotplug out CPU0, insert
> cpufreq driver and that will try to find these properties in CPU1.

OK, I see the possibility although it is still far away from use
cases. You cannot hotplug booting CPU (CPU0) on Exynos kernels. It
never worked. Strictly speaking - offlining will work. But bringing it
online will likely hang the system.

Best regards,
Krzysztof