linux-kernel - Re: [PATCH 2/2] cpufreq: CPPC: Fix error handling in cppc_scale_freq

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Message-ID: <8aa1efad-8f30-9548-259a-09fccb9da48a@hisilicon.com>
Date: Wed, 13 Aug 2025 15:15:12 +0800
From: Jie Zhan <zhanjie9@...ilicon.com>
To: Prashant Malani <pmalani@...gle.com>
CC: Viresh Kumar <viresh.kumar@...aro.org>, Bowen Yu <yubowen8@...wei.com>,
	<rafael@...nel.org>, <linux-pm@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <linuxarm@...wei.com>,
	<jonathan.cameron@...wei.com>, <lihuisong@...wei.com>,
	<zhenglifeng1@...wei.com>, Beata Michalska <beata.michalska@....com>, Ionela
 Voinescu <ionela.voinescu@....com>
Subject: Re: [PATCH 2/2] cpufreq: CPPC: Fix error handling in
 cppc_scale_freq_workfn()



On 05/08/2025 12:58, Prashant Malani wrote:
> On Mon, 4 Aug 2025 at 18:12, Prashant Malani <pmalani@...gle.com> wrote:
>>
>> On Sun, 3 Aug 2025 at 23:21, Jie Zhan <zhanjie9@...ilicon.com> wrote
>>> On 01/08/2025 16:58, Prashant Malani wrote:
>>>> This begs the question: why is this work function being scheduled
>>>> for CPUs that are in reset or offline/powered-down at all?
>>>> IANAE but it sounds like it would be better to add logic to ensure this
>>>> work function doesn't get scheduled/executed for CPUs that
>>>> are truly offline/powered-down or in reset.
>>> Yeah good question.  We may discuss that on your thread.
>>
>> OK.
>> Quickly looking around, it sounds having in the CPPC tick function [1]
>> might be a better option (one probably doesn't want to lift it beyond the
>> CPPC layer, since other drivers might have different behaviour).
>> One can add a cpu_online/cpu_enabled check there.
> 
> Fixed link:
> [1] https://elixir.bootlin.com/linux/v6.13/source/drivers/cpufreq/cppc_cpufreq.c#L125
I don't think a cpu_online/cpu_enabled check there would help.

Offlined CPUs don't make cppc_scale_freq_workfn() fail because they won't
have FIE triggered.  It fails from accessing perf counters on powered-down
CPUs.

Perhaps the CPPC FIE needs a bit rework.  AFAICS, FIE is meant to run in
ticks, but currently the CPPC FIE eventually runs in a thread due to the
possible PCC path when reading CPC regs I guess.