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

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Date:   Fri, 8 Feb 2019 12:09:49 +0000
From:   Sudeep Holla <sudeep.holla@....com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     Viresh Kumar <viresh.kumar@...aro.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 08, 2019 at 01:03:10PM +0100, Rafael J. Wysocki wrote:
> On Fri, Feb 8, 2019 at 12:39 PM Sudeep Holla <sudeep.holla@....com> wrote:
> >
> > On Fri, Feb 08, 2019 at 11:42:20AM +0100, Rafael J. Wysocki 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.
> >
> > I agree. The reason we don't see this generally on boot is because all
> > the CPUs are brought online before CPUfreq is initialised. While during
> > system suspend, we call cpufreq_online which in turn calls ->init in
> > the hotplug state machine.
> >
> > So as Rafael suggests we need to do some trick, but can it be done in
> > the core itself ? I may be missing something, but how about the patch
> > below:
> >
> > Regards,
> > Sudeep
> >
> > --
> > diff --git i/drivers/cpufreq/cpufreq.c w/drivers/cpufreq/cpufreq.c
> > index e35a886e00bc..7d8b0b99f91d 100644
> > --- i/drivers/cpufreq/cpufreq.c
> > +++ w/drivers/cpufreq/cpufreq.c
> > @@ -1241,7 +1241,8 @@ static int cpufreq_online(unsigned int cpu)
> >                 policy->max = policy->user_policy.max;
> >         }
> >
> > -       if (cpufreq_driver->get && !cpufreq_driver->setpolicy) {
> > +       if (cpufreq_driver->get && !cpufreq_driver->setpolicy &&
> > +           !cpufreq_suspended) {
> >                 policy->cur = cpufreq_driver->get(policy->cpu);
> >                 if (!policy->cur) {
> >                         pr_err("%s: ->get() failed\n", __func__);
> 
> It looks like we need to skip the "initial freq check" block below.
> 

Indeed, copy pasted an earlier version of diff. I found that I even
used a goto label wrong which I fixed along with the additional check
in "initial freq check" when I tried to compile :).

> Also this doesn't really help the case when the driver ->init() messes
> up with things.
>

Yes, in that case additional logic in the driver also needed. I am fine
if we enforce driver to deal with this issue, but was thinking if we can
make it generic. Also I was just trying to avoid adding _suspend/resume
to driver just to avoid this issue.

--
Regards,
Sudeep