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

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Message-ID: <20230331142724.ogvruad7txfe7ji2@bogus>
Date:   Fri, 31 Mar 2023 15:27:24 +0100
From:   Sudeep Holla <sudeep.holla@....com>
To:     Wing Li <wingers@...gle.com>
Cc:     Ulf Hansson <ulf.hansson@...aro.org>,
        Maulik Shah <quic_mkshah@...cinc.com>, andersson@...nel.org,
        dianders@...omium.org, swboyd@...omium.org,
        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, Mar 30, 2023 at 06:40:03PM -0700, Wing Li wrote:
> Adding some clarifications.
> 
> On Thu, Mar 30, 2023 at 6:13 AM Sudeep Holla <sudeep.holla@....com> wrote:
> 
> > On Thu, Mar 30, 2023 at 02:06:19PM +0200, Ulf Hansson wrote:
> > > 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.
> >
> 
> The spec quoted above only applies when switching from platform-coordinated
> mode to OS-initiated mode.
> 
> For switching from OS-initiated to platform-coordinated, which is the case
> Maulik is referring to, section 5.20.2 of the spec specifies:
> "A switch from OS-initiated mode to platform-coordinated mode is only
> possible if all cores other than the calling one are OFF, either through a
> call to CPU_OFF or not yet booted."
> 
>

My bad, I read/imagined it as PC->OSI mode couple of times even though it
is pretty explicit. Sorry for that. And thanks a lot for pointing that out.

-- 
Regards,
Sudeep