linux-kernel - Re: [PATCH 0/2] cpufreq/opp: rework regulator initialization

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Message-ID: <CAJZ5v0ih+CgYtt5FFb0thCEkCMpXfQHFaLugCOf_FAikCHgK6w@mail.gmail.com>
Date:   Fri, 8 Feb 2019 11:52:38 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Linux Samsung SoC <linux-samsung-soc@...r.kernel.org>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Nishanth Menon <nm@...com>, Stephen Boyd <sboyd@...nel.org>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Dave Gerlach <d-gerlach@...com>,
        Wolfram Sang <wsa@...-dreams.de>
Subject: Re: [PATCH 0/2] cpufreq/opp: rework regulator initialization

On Fri, Feb 8, 2019 at 11:42 AM Rafael J. Wysocki <rafael@...nel.org> wrote:
>
> On Fri, Feb 8, 2019 at 11:31 AM Viresh Kumar <viresh.kumar@...aro.org> wrote:
> >
> > On 08-02-19, 11:22, Rafael J. Wysocki wrote:
> > > There are cpufreq driver suspend and resume callbacks, maybe use them?
> > >
> > > The driver could do the I2C transactions in its suspend/resume
> > > callbacks and do nothing in online/offline if those are part of
> > > system-wide suspend/resume.
> >
> > These are per-policy things that we need to do, not sure if driver
> > suspend/resume is a good place for that. It is more for a case where
> > CPU 0-3 are in one policy and 4-7 in another. Now 1-7 are
> > hot-unplugged during system suspend and hotplugged later on. This is
> > more like complete removal/addition of devices instead of
> > suspend/resume.
>
> No, it isn't.  We don't remove devices on offline.  We migrate stuff
> away from them and (opportunistically) power them down.
>
> If this is system suspend, the driver kind of knows that offline will
> take place, so it can prepare for it.  Likewise, when online takes
> place during system-wide resume, it generally is known that this is
> system-wide resume (there is a flag to indicate that in CPU hotplug),
> it can be "smart" and avoid accessing suspended devices.  Deferring
> the frequency set up until the driver resume time should do the trick
> I suppose.

BTW, do transitions to idle states involve I2C transactions on the
systems in question?