linux-kernel - Re: [PATCH 0/2] Add provision to keep idle state disabled

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Date:   Wed, 21 Jun 2023 11:51:19 +0530
From:   Tushar Nimkar <quic_tnimkar@...cinc.com>
To:     Ulf Hansson <ulf.hansson@...aro.org>
CC:     "Rafael J . Wysocki" <rafael@...nel.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        <linux-pm@...r.kernel.org>, <linux-arm-msm@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <quic_lsrao@...cinc.com>,
        <quic_mkshah@...cinc.com>
Subject: Re: [PATCH 0/2] Add provision to keep idle state disabled

Many thanks again,

On 6/16/2023 4:25 PM, Ulf Hansson wrote:
> On Wed, 14 Jun 2023 at 08:43, Tushar Nimkar <quic_tnimkar@...cinc.com> wrote:

> 
> Right. I am not saying it's the perfect solution, but it seems like it
> could potentially solve the problem for many cases.
> 
> If you want some help to turn the cpuidle-psci driver into a loadable
> module, just reach out, I am happy to help.
> 
Thanks :)
Making cpuidle-psci as loadable does not hold good for target does not 
support DLKM, in addition to it rpmh driver has dependency on 
cpuidle-psci for pm-domain and rpmh probe will get defer, their are 
driver which depends on rpmh probe like interconnect, clk etc. And 
eventually dependent driver probe defers which are essential for Linux 
boot-up.
Hope you got scenario for getting probe defer if we make cpuidle-psci as 
loadable.

I have below options as well
[A]: Can we think of making "governor/param_governor" 
module_param_string, string named governor only to load. In that way 
need to remove check [3]. Let's say string passed as "teo" then it will 
not load "menu" and loads "teo" once comes-up.

[B]: Can we think of making cpuidle.off as writable, let governors to 
register (i.e remove check [4]) and allow cpuidle_init() to happen (i.e 
remove check [5])
So in this way cpuidle.off=1, your idle state can not be selected 
because [6] and later we can write off=0 to let same check [6] to fail.

[C]: Coming to this series approach...What is best way to utilize 
already present Flag-CPUIDLE_FLAG_OFF ?
Since we can not add new DT property to take decision in driver as it's 
not HW feature to be expose in device tree [7]. Can we introduce new 
module_param() for making idle-state disable default and utilize 
CPUIDLE_FLAG_OFF? maybe similar to [8]

happy to hear your thoughts!

[3] 
https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/tree/drivers/cpuidle/governor.c?h=next-20230620#n93

[4] 
https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/tree/drivers/cpuidle/governor.c?h=next-20230620#n86

[5] 
https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/tree/drivers/cpuidle/cpuidle.c?h=next-20230620#n808

[6] 
https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/tree/kernel/sched/idle.c?h=next-20230620#n167

[7] 
https://lore.kernel.org/lkml/20230608085544.16211-1-quic_tnimkar@quicinc.com/T/#m5d6012b0dfcff700f48c0efbba629382f18ee33b

[8] 
https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/tree/drivers/idle/intel_idle.c?h=next-20230620#n2160
> [...]
> 
> Kind regards
> Uffe

Thanks,
Tushar