linux-kernel - Re: [PATCH 2/2] arm64: dts: qcom: SM8750: Enable CPUFreq support

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Message-ID: <99796cc0-f29b-40d0-b8bb-ebcbcc950b23@oss.qualcomm.com>
Date: Tue, 20 Jan 2026 15:43:49 +0100
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: Akhil P Oommen <akhilpo@....qualcomm.com>,
        Jagadeesh Kona <jagadeesh.kona@....qualcomm.com>
Cc: Ajit Pandey <ajit.pandey@....qualcomm.com>,
        Imran Shaik <imran.shaik@....qualcomm.com>,
        Taniya Das <taniya.das@....qualcomm.com>,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org, Sibi Sankar <sibi.sankar@....qualcomm.com>,
        Jassi Brar <jassisinghbrar@...il.com>, Rob Herring <robh@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Conor Dooley
 <conor+dt@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konradybcio@...nel.org>
Subject: Re: [PATCH 2/2] arm64: dts: qcom: SM8750: Enable CPUFreq support

On 1/20/26 12:25 PM, Akhil P Oommen wrote:
> On 1/20/2026 3:44 PM, Konrad Dybcio wrote:
>> On 1/19/26 8:00 PM, Akhil P Oommen wrote:
>>> On 12/11/2025 12:32 AM, Jagadeesh Kona wrote:
>>>> Add the cpucp mailbox, sram and SCMI nodes required to enable
>>>> the CPUFreq support using the SCMI perf protocol on SM8750 SoCs.
>>>>
>>>> Signed-off-by: Jagadeesh Kona <jagadeesh.kona@....qualcomm.com>
>>>
>>> Just curious, does this patch enable thermal mitigation for CPU clusters
>>> too?
>>
>> If nothing changed, we have lets-not-explode type mitigations via LMH,
>> but lets-not-burn-the-user would require a skin temp sensor to be
>> wired up, which then could be used to enable some cooling action
> 
> In some chipsets, I have noticed that the gpu cooling device throttles
> GPU to the lowest OPP even with not-so-heavy GPU workloads, making it
> unusable-ly slow. My hypothesis was that it was due to unmitigated CPU
> temperature tripping up GPU Tsens.
> 
> So, I am wondering if there are any additional CPU cooling related
> changes required to get a reasonable overall performance under thermal
> constraints.

Yes, something like the aforementioned skin-temp sensor at least..

Today Linux will not throttle the CPUs at all (they're not even declared
as cooling devices) and we sorta agreed that in general it's a good thing
(tm), because otherwise we'd be coding in a cooling profile into the SoC
DTSI without taking into account the cooling capabilities of a given end
device (i.e. in an extreme case, a PC with SM8650 with a cooler that's
3kg of aluminium vs a Steam Frame headset where the SoC is centimeters
away from your face)

Currently, we have cooling policies for devices with fans and the only
other action is based on a skin temperature sensor (sc8280xp + x13s).
Everything else is left up to the LMH defaults. AFAIK work is ongoing to
create a more informed solution, that would have to (quite obviously)
live in userland.

Konrad