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

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Date:   Fri, 8 Feb 2019 11:39:04 +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>,
        Sudeep Holla <sudeep.holla@....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 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__);
@@ -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;
+               }
        }
 }