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

Sudeep Holla
2019-02-08T11:39:04Z

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__);
@@ -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;
+ }
}
}