linux-kernel - Re: [PATCH v3 1/2] arm64: dts: qcom: sm8650: drop cpu thermal passive trip points

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Message-ID: <80948a6f-1cd4-47b3-9218-f5ab0c25eb3b@oss.qualcomm.com>
Date: Sat, 1 Feb 2025 16:41:22 +0100
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: Neil Armstrong <neil.armstrong@...aro.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konradybcio@...nel.org>, Rob Herring <robh@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Conor Dooley <conor+dt@...nel.org>
Cc: linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/2] arm64: dts: qcom: sm8650: drop cpu thermal passive
 trip points

On 29.01.2025 10:43 AM, Neil Armstrong wrote:
> On the SM8650, the dynamic clock and voltage scaling (DCVS) is done in an
> hardware controlled loop using the LMH and EPSS blocks with constraints and
> OPPs programmed in the board firmware.
> 
> Since the Hardware does a better job at maintaining the CPUs temperature
> in an acceptable range by taking in account more parameters like the die
> characteristics or other factory fused values, it makes no sense to try
> and reproduce a similar set of constraints with the Linux cpufreq thermal
> core.
> 
> In addition, the tsens IP is responsible for monitoring the temperature
> across the SoC and the current settings will heavily trigger the tsens
> UP/LOW interrupts if the CPU temperatures reaches the hardware thermal
> constraints which are currently defined in the DT. And since the CPUs
> are not hooked in the thermal trip points, the potential interrupts and
> calculations are a waste of system resources.
> 
> Drop the current passive trip points and only leave the critical trip
> point that will trigger a software system reboot before an hardware
> thermal shutdown in the allmost impossible case the hardware DCVS cannot
> handle the temperature surge.
> 
> Signed-off-by: Neil Armstrong <neil.armstrong@...aro.org>
> ---
>  arch/arm64/boot/dts/qcom/sm8650.dtsi | 180 -----------------------------------
>  1 file changed, 180 deletions(-)
> 
> diff --git a/arch/arm64/boot/dts/qcom/sm8650.dtsi b/arch/arm64/boot/dts/qcom/sm8650.dtsi
> index 25e47505adcb790d09f1d2726386438487255824..95509ce2713d4fcc3dbe0c5cd5827312d5681af4 100644
> --- a/arch/arm64/boot/dts/qcom/sm8650.dtsi
> +++ b/arch/arm64/boot/dts/qcom/sm8650.dtsi
> @@ -5751,18 +5751,6 @@ cpu2-top-thermal {
>  			thermal-sensors = <&tsens0 5>;
>  
>  			trips {
> -				trip-point0 {
> -					temperature = <90000>;
> -					hysteresis = <2000>;
> -					type = "passive";
> -				};

Feel free to drop polling-delay-passive from these nodes too

Konrad