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From:   "Rafael J. Wysocki" <rafael@kernel.org>
Date:   Fri, 8 Feb 2019 13:03:10 +0100
Message-ID: <CAJZ5v0gbh2LDq+6P_CQ+GWOxEdQrRUqQnx7v59hvs2_wwx9=kw@mail.gmail.com>
Subject: Re: [PATCH 0/2] cpufreq/opp: rework regulator initialization
To:     Sudeep Holla <sudeep.holla@arm.com>
Cc:     "Rafael J. Wysocki" <rafael@kernel.org>,
        Viresh Kumar <viresh.kumar@linaro.org>,
        Marek Szyprowski <m.szyprowski@samsung.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linux PM <linux-pm@vger.kernel.org>,
        Linux Samsung SoC <linux-samsung-soc@vger.kernel.org>,
        "Rafael J . Wysocki" <rjw@rjwysocki.net>,
        Nishanth Menon <nm@ti.com>, Stephen Boyd <sboyd@kernel.org>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>,
        Dave Gerlach <d-gerlach@ti.com>,
        Wolfram Sang <wsa@the-dreams.de>
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On Fri, Feb 8, 2019 at 12:39 PM Sudeep Holla <sudeep.holla@arm.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@linaro.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.

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

> @@ -1702,6 +1703,11 @@ void cpufreq_resume(void)
>                                 pr_err("%s: Failed to start governor for policy: %p\n",
>                                        __func__, policy);
>                 }
> +               policy->cur = cpufreq_driver->get(policy->cpu);
> +               if (!policy->cur) {
> +                       pr_err("%s: ->get() failed\n", __func__);
> +                       goto out_destroy_policy;
> +               }
>         }
>  }
>