linux-kernel - Re: [PATCH v2 1/2] devfreq: qcom: Add L2 Krait Cache devfreq scaling driver

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Message-ID: <20200930092954.GA7125@bogus>
Date:   Wed, 30 Sep 2020 10:29:54 +0100
From:   Sudeep Holla <sudeep.holla@....com>
To:     Ansuel Smith <ansuelsmth@...il.com>
Cc:     Rob Herring <robh+dt@...nel.org>, Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        MyungJoo Ham <myungjoo.ham@...sung.com>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        Sudeep Holla <sudeep.holla@....com>,
        Chanwoo Choi <cw00.choi@...sung.com>,
        linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org
Subject: Re: [PATCH v2 1/2] devfreq: qcom: Add L2 Krait Cache devfreq scaling
 driver

On Tue, Sep 29, 2020 at 06:29:24PM +0200, Ansuel Smith wrote:
> Qcom L2 Krait CPUs use the generic cpufreq-dt driver and doesn't actually
> scale the Cache frequency when the CPU frequency is changed. This
> devfreq driver register with the cpu notifier and scale the Cache
> based on the max Freq across all core as the CPU cache is shared across
> all of them. If provided this also scale the voltage of the regulator
> attached to the CPU cache. The scaling logic is based on the CPU freq
> and the 3 scaling interval are set by the device dts.
>

I have raised this concern before. I am worried this kind of independent
CPU and cache frequency controls make way for clkscrew kind of attacks.
Why can't the clocks be made parent/child or secondary and automatically
updated when CPU clocks are changed.

-- 
Regards,
Sudeep