linux-kernel - Re: [PATCH v2 1/2] cpuidle: psci: Move enabling OSI mode after power domains creation

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Date:   Thu, 30 Mar 2023 14:06:19 +0200
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Sudeep Holla <sudeep.holla@....com>
Cc:     Maulik Shah <quic_mkshah@...cinc.com>, andersson@...nel.org,
        dianders@...omium.org, swboyd@...omium.org, wingers@...gle.com,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org, jwerner@...omium.org,
        quic_lsrao@...cinc.com, quic_rjendra@...cinc.com
Subject: Re: [PATCH v2 1/2] cpuidle: psci: Move enabling OSI mode after power
 domains creation

On Thu, 30 Mar 2023 at 11:34, Sudeep Holla <sudeep.holla@....com> wrote:
>
> On Thu, Mar 30, 2023 at 02:12:49PM +0530, Maulik Shah wrote:
> > A switch from OSI to PC mode is only possible if all CPUs other than the
> > calling one are OFF, either through a call to CPU_OFF or not yet booted.
> >
>
> As per the spec, all cores are in one of the following states:
>  - Running
>  - OFF, either through a call to CPU_OFF or not yet booted
>  - Suspended, through a call to CPU_DEFAULT_SUSPEND
>
> Better to provide full information.
>
> > Currently OSI mode is enabled before power domains are created. In cases
> > where CPUidle states are not using hierarchical CPU topology the bail out
> > path tries to switch back to PC mode which gets denied by firmware since
> > other CPUs are online at this point and creates inconsistent state as
> > firmware is in OSI mode and Linux in PC mode.
> >
>
> OK what is the issue if the other cores are online ? As long as they are
> running, it is allowed in the spec, so your statement is incorrect.
>
> Is CPUidle enabled before setting the OSI mode. I see only that can cause
> issue as we don't use CPU_DEFAULT_SUSPEND. If idle is not yet enabled, it
> shouldn't be a problem.

Sudeep, you may very well be correct here. Nevertheless, it looks like
the current public TF-A implementation doesn't work exactly like this,
as it reports an error in Maulik's case. We should fix it too, I
think.

Although, to me it doesn't really matter as I think $subject patch
makes sense anyway. It's always nice to simplify code when it's
possible.

Note also that, before commit 70c179b49870 ("cpuidle: psci: Allow PM
domain to be initialized even if no OSI mode"), it made sense to call
psci_pd_try_set_osi_mode() before creating the genpds, but beyond that
it doesn't really matter anymore.

Kind regards
Uffe