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

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Date:   Fri, 8 Feb 2019 11:42:20 +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 11:31 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.