linux-kernel - Re: [PATCH v1 6/7] arm64: dts: sdm845: Increase alert trip point to 95 degrees

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Message-ID: <CAHLCerOVyOUvvXHRQFpn29=ycy4VZHocsNdHbcR4ZK4RfGq49A@mail.gmail.com>
Date:   Fri, 11 Jan 2019 01:36:20 +0530
From:   Amit Kucheria <amit.kucheria@...aro.org>
To:     Stephen Boyd <swboyd@...omium.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Eduardo Valentin <edubezval@...il.com>,
        Andy Gross <andy.gross@...aro.org>,
        Taniya Das <tdas@...eaurora.org>,
        Douglas Anderson <dianders@...omium.org>,
        Matthias Kaehlcke <mka@...omium.org>,
        David Brown <david.brown@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>
Subject: Re: [PATCH v1 6/7] arm64: dts: sdm845: Increase alert trip point to
 95 degrees

On Thu, Jan 10, 2019 at 5:59 AM Stephen Boyd <swboyd@...omium.org> wrote:
>
> Quoting Amit Kucheria (2019-01-09 16:00:55)
> > 75 degrees is too aggressive for throttling the CPU. After speaking to
> > Qualcomm engineers, increase it to 95 degrees.
> >
> > Signed-off-by: Amit Kucheria <amit.kucheria@...aro.org>
> > ---
> >  arch/arm64/boot/dts/qcom/sdm845.dtsi | 16 ++++++++--------
>
> Is the plan that these are some defaults that would be adjusted by board
> variants? Just curious why we have anything in here and don't punt it
> all to each board dts file.

These values are meant to be safe values for silicon operation as
characterised[1] by the HW team. So I'd consider them a more than just
default values. It also gives future boards a safe starting point.

IMHO it would be better to have the characterized values merged
upstream and if really required, those values can be tweaked in the
board-specific DTS.

[1] Caveat: The characterisation probably focused on mobile devices
and might change depending on form-factor, active cooling and heat
dissipation design but those differences should only impact the skin
temperature, not the operation of the SoC itself.