linux-kernel - Re: [PATCH 09/19] arm: dts: qcom: sdx55/sdx65: Fix CPU power-domain-names

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Message-ID: <Z_dvAT7LdR7xbH45@linaro.org>
Date: Thu, 10 Apr 2025 09:10:57 +0200
From: Stephan Gerhold <stephan.gerhold@...aro.org>
To: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
Cc: Ulf Hansson <ulf.hansson@...aro.org>,
	"Rob Herring (Arm)" <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>, Chen-Yu Tsai <wens@...e.org>,
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	Lorenzo Pieralisi <lpieralisi@...nel.org>,
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	Konrad Dybcio <konradybcio@...nel.org>,
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	Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
Subject: Re: [PATCH 09/19] arm: dts: qcom: sdx55/sdx65: Fix CPU
 power-domain-names

On Wed, Apr 09, 2025 at 08:35:29PM +0200, Konrad Dybcio wrote:
> On 4/7/25 6:27 PM, Ulf Hansson wrote:
> > On Fri, 4 Apr 2025 at 22:41, Konrad Dybcio
> > <konrad.dybcio@....qualcomm.com> wrote:
> >>
> >> On 4/4/25 4:59 AM, Rob Herring (Arm) wrote:
> >>> "rpmhpd" is not documented nor used anywhere. As the enable-method is
> >>> "psci" use "psci" for the power-domain name.
> >>>
> >>> Signed-off-by: Rob Herring (Arm) <robh@...nel.org>
> >>> ---
> >>
> >> "psci" is what we want here, but these platforms require some more
> >> massaging..
> > 
> > So this isn't for CPU performance scaling?
> 
> Nope!
> 

Huh, this is definitely "perf" (= cpufreq) and not "psci" (= cpuidle).
If you run blame on this line you get to:

commit 0ec7bde7b590f8efa5823df3b52b32dd373060ff
Author: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
Date:   Thu Apr 8 22:34:45 2021 +0530

    ARM: dts: qcom: sdx55: Add CPUFreq support

    Add CPUFreq support to SDX55 platform using the cpufreq-dt driver.
    There is no dedicated hardware block available on this platform to
    carry on the CPUFreq duties. Hence, it is accomplished using the CPU
    clock and regulators tied together by the operating points table.

https://web.git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=0ec7bde7b590f8efa5823df3b52b32dd373060ff

The OPP table looks like it's supposed to set SDX55_CX performance
states according to the chosen CPU frequency. MSM8909 has a similar
setup where the CPU is supplied directly by VDDCX and we describe that
with "perf" too [1].

What I don't understand is why the name "rpmhpd" does not appear
in any driver. The MSM8909 setup goes via qcom-cpufreq-nvmem, where
"perf" is directly assigned for cpufreq scaling. I can only think of two
possible reasons:

 - The power domain is implicitly attached to the OPP table(?), because
   there is just a single power domain defined on the CPU, or

 - This was never working correctly.

For both cases, I think it would be best to change the power domain name
to "perf" like Uffe suggested.

Thanks,
Stephan

[1]: https://lore.kernel.org/linux-pm/20231018-msm8909-cpufreq-v2-0-0962df95f654@kernkonzept.com/