Re: [PATCH] cpufreq: skip cpufreq resume if it's not suspended

[Bo Yan]

On 02/02/2018 11:34 AM, Saravana Kannan wrote:
> On 02/02/2018 03:54 AM, Rafael J. Wysocki wrote:
> > On Wednesday, January 24, 2018 9:53:14 PM CET Bo Yan wrote:
> > > On 01/23/2018 06:02 PM, Rafael J. Wysocki wrote:
> > > > On Tuesday, January 23, 2018 10:57:55 PM CET Bo Yan wrote:
> > > > > ÂÂ drivers/cpufreq/cpufreq.c | 4 ++++
> > > > > ÂÂ 1 file changed, 4 insertions(+)
> > > > >
> > > > > diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> > > > > index 41d148af7748..95b1c4afe14e 100644
> > > > > --- a/drivers/cpufreq/cpufreq.c
> > > > > +++ b/drivers/cpufreq/cpufreq.c
> > > > > @@ -1680,6 +1680,10 @@ void cpufreq_resume(void)
> > > > > ÂÂÂÂÂÂ if (!cpufreq_driver)
> > > > > ÂÂÂÂÂÂÂÂÂÂ return;
> > > > >
> > > > > +ÂÂÂ if (unlikely(!cpufreq_suspended)) {
> > > > > +ÂÂÂÂÂÂÂ pr_warn("%s: resume after failing suspend\n", __func__);
> > > > > +ÂÂÂÂÂÂÂ return;
> > > > > +ÂÂÂ }
> > > > > ÂÂÂÂÂÂ cpufreq_suspended = false;
> > > > >
> > > > > ÂÂÂÂÂÂ if (!has_target() && !cpufreq_driver->resume)
> > > > Good catch, but rather than doing this it would be better to avoid
> > > > calling cpufreq_resume() at all if cpufreq_suspend() has not been 
> > > > called.
> > > Yes, I thought about that, but there is no good way to skip over it
> > > without introducing another flag. cpufreq_resume is called by
> > > dpm_resume, cpufreq_suspend is called by dpm_suspend. In the failure
> > > case, dpm_resume is called, but dpm_suspend is not. So on a higher 
> > > level
> > > it's already unbalanced.
> > >
> > > One possibility is to rely on the pm_transition flag. So something 
> > > like:
> > >
> > >
> > > diff --git a/drivers/base/power/main.c b/drivers/base/power/main.c
> > > index dc259d20c967..8469e6fc2b2c 100644
> > > --- a/drivers/base/power/main.c
> > > +++ b/drivers/base/power/main.c
> > > @@ -842,6 +842,7 @@ static void async_resume(void *data, async_cookie_t
> > > cookie)
> > > ÂÂ void dpm_resume(pm_message_t state)
> > > ÂÂ {
> > > ÂÂÂÂÂÂÂÂÂ struct device *dev;
> > > +ÂÂÂÂÂÂ bool suspended = (pm_transition.event != PM_EVENT_ON);
> > > ÂÂÂÂÂÂÂÂÂ ktime_t starttime = ktime_get();
> > >
> > > ÂÂÂÂÂÂÂÂÂ trace_suspend_resume(TPS("dpm_resume"), state.event, true);
> > > @@ -885,7 +886,8 @@ void dpm_resume(pm_message_t state)
> > > ÂÂÂÂÂÂÂÂÂ async_synchronize_full();
> > > ÂÂÂÂÂÂÂÂÂ dpm_show_time(starttime, state, NULL);
> > >
> > > -ÂÂÂÂÂÂ cpufreq_resume();
> > > +ÂÂÂÂÂÂ if (likely(suspended))
> > > +ÂÂÂÂÂÂÂÂÂÂÂÂÂÂ cpufreq_resume();
> > > ÂÂÂÂÂÂÂÂÂ trace_suspend_resume(TPS("dpm_resume"), state.event, false);
> > > ÂÂ }
> >
> > I was thinking about something else.
> >
> > Anyway, I think your original patch is OK too, but without printing the
> > message. Just combine the cpufreq_suspended check with the 
> > cpufreq_driver
> > one and the unlikely() thing is not necessary.
>
> I rather have this fixed in the dpm_suspend/resume() code. This is 
> just masking the first issue that's being caused by unbalanced error 
> handling. If that means adding flags in dpm_suspend/resume() then 
> that's what we should do right now and clean it up later if it can be 
> improved. Making cpufreq more messy doesn't seem like the right answer.
>
> Thanks,
> Saravana
dpm_suspend and dpm_resume by themselves are not balanced in this 
particular case. As it's currently structured, dpm_resume can't be 
omitted even if dpm_suspend is skipped due to earlier failure. I think 
checking cpufreq_suspended flag is a reasonable compromise. If we can 
find a way to make dpm_suspend/dpm_resume also balanced, that will be best.