linux-kernel - Re: [PATCH 3/3] arm64: dts: qcom: ipq5018: enable the CPUFreq support

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Date:   Wed, 30 Aug 2023 22:42:29 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Gokul Sriram P <quic_gokulsri@...cinc.com>
Cc:     Robert Marko <robimarko@...il.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        agross@...nel.org, andersson@...nel.org, konrad.dybcio@...aro.org,
        mturquette@...libre.com, sboyd@...nel.org, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, jassisinghbrar@...il.com,
        linux-arm-msm@...r.kernel.org, linux-clk@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        quic_varada@...cinc.com, quic_srichara@...cinc.com
Subject: Re: [PATCH 3/3] arm64: dts: qcom: ipq5018: enable the CPUFreq support

On Wed, 30 Aug 2023 at 21:32, Gokul Sriram P <quic_gokulsri@...cinc.com> wrote:
>
>
> >>>>>    #include <dt-bindings/interrupt-controller/arm-gic.h>
> >>>>>    #include <dt-bindings/clock/qcom,gcc-ipq5018.h>
> >>>>>    #include <dt-bindings/reset/qcom,gcc-ipq5018.h>
> >>>>> +#include <dt-bindings/clock/qcom,apss-ipq.h>
> >>>> c is before r.
>   Sure, will update.
>
> [...]
> >>>>
> >>>>> +   cpu_opp_table: opp-table-cpu {
> >>>>> +           compatible = "operating-points-v2";
> >>>>> +           opp-shared;
> >>>>> +
> >>>>> +           opp-1008000000 {
> >>>>> +                   opp-hz = /bits/ 64 <1008000000>;
> >>>>> +                   opp-microvolt = <1100000>;
> >>>>> +                   clock-latency-ns = <200000>;
> >>>> And the rest of OPPs?
> >>> Hi Krzysztof,
> >>> IPQ5018 only supports running at 1.1GHz, but its running at 800MHz
> >>> by default from the bootloader so there is only one OPP.
> >> Isn't this contradictory? If it is running at 800 initially, then it
> >> supports running at 800...
> > I can only guess that it's not validated at 800MHz.
> As per the h/w design team, there is negligible power or thermal benefit
> by lowering to 800MHz clock.
> Hence, 800MHz opp wasn't included here.

Just my 2c. If 800 MHz is supported, it should be included. Even if
just to prevent the kernel from throwing a warning about the CPU
running at the unsupported frequency. Then one can use scheduler
tunings to prevent the CPU from going to 800 MHz state.


-- 
With best wishes
Dmitry