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

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Message-ID: <CAPDyKFqKw-6Qu7YoZw9LQDGvj1PFi3nCDkXcmCJTffxtX75naQ@mail.gmail.com>
Date:   Thu, 22 Jun 2023 15:01:40 +0200
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Tushar Nimkar <quic_tnimkar@...cinc.com>
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

On Wed, 21 Jun 2023 at 08:21, Tushar Nimkar <quic_tnimkar@...cinc.com> wrote:
>
> 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 :)

Np!

> 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 understand your concern, but you have got my idea wrong.

I was suggesting turning the cpuidle-psci driver into a loadable
module - not the cpuidle-psci-domain driver. The latter is the genpd
provider, which consumers like rpmh need to probe.

>
> 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!

In general I am not in favor of module parameters, but maybe it's the
best option to solve this problem. We need Rafael's and Daniel's
opinion to conclude.

However, to me, I still think the easiest approach would be to turn
the cpuidle-psci driver into a loadable module. Let me hack on that
and post a few patches that you can test for this.

>
>
> [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