linux-kernel - Re: [PATCH 0/2] arm64: dts: qcom: sm8650: rework CPU & GPU thermal zones

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Message-ID: <b305ec90-26b6-4dfa-830a-4ff3acd9caf5@oss.qualcomm.com>
Date: Fri, 3 Jan 2025 15:43:04 +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 0/2] arm64: dts: qcom: sm8650: rework CPU & GPU thermal
 zones

On 3.01.2025 3:38 PM, Neil Armstrong wrote:
> On the SM8650 platform, the dynamic clock and voltage scaling (DCVS) for
> the CPUs and GPU is handled by hardware & firmware using factory and
> form-factor determined parameters in order to maximize frequency while
> keeping the temperature way below the junction temperature where the SoC
> would experience a thermal shutdown if not permanent damages.
> 
> On the other side, the High Level Ooperating System (HLOS), like Linux,
> is able to adjust the CPU and GPU frequency using the internal SoC
> temperature sensors (here tsens) and it's UP/LOW interrupts, but it
> effectly does the same work twice in an less effective manner.
> 
> Let's take the Hardware & Firmware action in account and design the
> thermal zones trip points and cooling devices mapping to use the HLOS
> as a safety warant in case the platform experiences a temperature surge
> to helpfully avoid a thermal shutdown and handle the scenario gracefully.
> 
> On the CPU side, the LMh hardware does the DCVS control loop, so
> let's set higher trip points temperatures closer to the junction
> and thermal shutdown temperatures and add some idle injection cooling
> device with 100% duty cycle for each CPU that would act as emergency
> action to avoid the thermal shutdown.
> 
> On the GPU side, the GPU Management Unit (GMU) acts as the DCVS
> control loop, but since we can't perform idle injection, let's
> also set higher trip points temperatures closer to the junction
> and thermal shutdown temperatures to reduce the GPU frequency only
> as an emergency action before the thermal shutdown.
> 
> Those 2 changes optimizes the thermal management design by avoiding
> concurrent thermal management, calculations & avoidable interrupts
> by moving the HLOS management to a last resort emergency if the
> Hardware & Firmwares fails to avoid a thermal shutdown.
> 
> Signed-off-by: Neil Armstrong <neil.armstrong@...aro.org>
> ---

Got any numbers to back this?

Konrad