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From:   Krzysztof Kozlowski <krzk@kernel.org>
Date:   Wed, 30 May 2018 14:32:12 +0200
Message-ID: <CAJKOXPftrzwLMSDeTBBxG-nvpsriBuPEwQAViTcE3DYRYsnzmg@mail.gmail.com>
Subject: Re: [PATCH 07/15] arm: dts: exynos: Add missing cooling device
 properties for CPUs
To:     Viresh Kumar <viresh.kumar@linaro.org>
Cc:     arm@kernel.org, Rob Herring <robh+dt@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Kukjin Kim <kgene@kernel.org>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        ionela.voinescu@arm.com,
        Daniel Lezcano <daniel.lezcano@linaro.org>,
        chris.redpath@arm.com, devicetree@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org,
        "linux-samsung-soc@vger.kernel.org" 
        <linux-samsung-soc@vger.kernel.org>, linux-kernel@vger.kernel.org
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On Wed, May 30, 2018 at 6:38 AM, Viresh Kumar <viresh.kumar@linaro.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