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

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Message-ID: <27ae4821-b185-41ba-a0ed-6e4f754a4484@oss.qualcomm.com>
Date: Thu, 9 Jan 2025 16:20:58 +0100
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: neil.armstrong@...aro.org, Konrad Dybcio
 <konrad.dybcio@....qualcomm.com>,
        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>, robclark@...edesktop.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 3:49 PM, Neil Armstrong wrote:
> On 03/01/2025 15:43, Konrad Dybcio wrote:
>> 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.

We could probably work out some mechanism for drm to say "gpu is too
hot / too busy" and stall the userspace's requests.. If that doesn't
exist already (+RobC)

>>>
>>> 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?
> 
> To back which part ? Yes I've been running loads with difference
> scenarios and effectively the hardware work is much better with
> a more linear correction and slighly better performances because
> it sets slighly higger OPPs while maintaining the core closer to
> the target temperature range. Which is kind of expected.
> 
> I don't have easy numbers to share, sorry...

Ok, what you said above sounds good already.

Konrad