linux-kernel - Re: [PATCH v5 6/6] arm64: dts: qcom: Enable cpu cooling devices for QCS9075 platforms

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Message-ID: <af982662-85c0-5d21-be40-44cbc8401678@quicinc.com>
Date: Tue, 31 Dec 2024 16:35:48 +0530
From: Manaf Meethalavalappu Pallikunhi <quic_manafm@...cinc.com>
To: Konrad Dybcio <konrad.dybcio@....qualcomm.com>,
        Wasim Nazir
	<quic_wasimn@...cinc.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>
CC: <linux-arm-msm@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <kernel@...cinc.com>
Subject: Re: [PATCH v5 6/6] arm64: dts: qcom: Enable cpu cooling devices for
 QCS9075 platforms


Hi Konrad,

On 12/30/2024 9:05 PM, Konrad Dybcio wrote:
> On 29.12.2024 4:23 PM, Wasim Nazir wrote:
>> From: Manaf Meethalavalappu Pallikunhi <quic_manafm@...cinc.com>
>>
>> In QCS9100 SoC, the safety subsystem monitors all thermal sensors and
>> does corrective action for each subsystem based on sensor violation
>> to comply safety standards. But as QCS9075 is non-safe SoC it
>> requires conventional thermal mitigation to control thermal for
>> different subsystems.
>>
>> The cpu frequency throttling for different cpu tsens is enabled in
>> hardware as first defense for cpu thermal control. But QCS9075 SoC
>> has higher ambient specification. During high ambient condition, even
>> lowest frequency with multi cores can slowly build heat over the time
>> and it can lead to thermal run-away situations. This patch restrict
>> cpu cores during this scenario helps further thermal control and
>> avoids thermal critical violation.
>>
>> Add cpu idle injection cooling bindings for cpu tsens thermal zones
>> as a mitigation for cpu subsystem prior to thermal shutdown.
>>
>> Add cpu frequency cooling devices that will be used by userspace
>> thermal governor to mitigate skin thermal management.
>>
>> Signed-off-by: Manaf Meethalavalappu Pallikunhi <quic_manafm@...cinc.com>
>> ---
> Does this bring measurable benefits over just making the CPU a cooling
> device and pointing the thermal zones to it (and not the idle subnode)?
>
> Konrad
As noted in the commit, CPU frequency mitigation is handled by hardware 
as a first level mitigation. The software/scheduler will be updated via 
arch_update_hw_pressure API [1] for this mitigation. Adding the same CPU 
mitigation in thermal zones is redundant. We are adding idle injection 
with a 100% duty cycle as an additional mitigation step  at higher trip 
to further reduce CPU power consumption. This helps device thermal 
stability further, especially in high ambient conditions.

[1]. 
https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/tree/drivers/cpufreq/qcom-cpufreq-hw.c?h=next-20241220#n352

Best regards,

Manaf