Re: [PATCH] PM: sleep: call devfreq_suspend/resume and cpufreq_suspend/resume in pairs.

[Rafael J. Wysocki]

On Wed, Apr 22, 2020 at 1:19 PM Chunyan Zhang <zhang.lyra@xxxxxxxxx> wrote:
>
> Hi Rafael,
>
> (Behalf Of Vincent Wang)
>
> Thanks for your comments, please see my answers below.
>
> On Wed, 22 Apr 2020 at 17:05, Rafael J. Wysocki <rafael@xxxxxxxxxx> wrote:
> >
> > On Wed, Apr 22, 2020 at 7:15 AM Chunyan Zhang <zhang.lyra@xxxxxxxxx> wrote:
> > >
> > > From: Vincent Wang <vincent.wang@xxxxxxxxxx>
> > >
> > > If dpm_prepare() fails in dpm_suspend_start(), dpm_suspend() can't be
> > > called.
> >
> > That's correct.
> >
> > > And then, devfreq_suspend() and cpufreq_suspend() will not be
> > > called in the suspend flow.
> >
> > Right.
> >
> > > But in the resiume flow, devfreq_resume() and cpufreq_resume() will
> > > be called.
> >
> > Right, and they are expected to cope with the situation.
> >
> > > This patch will ensure that devfreq_suspend/devfreq_resume and
> > > cpufreq_suspend/cpufreq_resume are called in pairs.
> >
> > So why is it better to do this than to make devfreq_resume() meet the
> > expectations?
>
> Yesïwe found an issue with cpufreq schedutil governor on kernel4.14,
> and I think the issue should haven't been changed on the latest
> version of kernel.
>
> In the function dpm_suspend_start(), dpm_suspend() would not be
> exceuted if return error from device_prepare() [1]. So
> cpufreq_cpufreq() will not be called,

I guess you mean cpufreq_suspend().

That should be OK .

> then cpufreq_remove_update_util_hook() will not be called either, and so
> cpufreq_update_util_data will not be NULL.
>
> In the dpm resume flow, sugov_start() will be called, in which
> sg_cpu.update_util will be set to 0.

Which code patch does this?

Surely not cpufreq_resume(), because that checks cpufreq_suspended which
cannot be set if cpufreq_suspend() has not been called (because it is the only
place setting cpufreq_suspended).