linux-kernel - Re: [RFC][PATCH 1/3] PM / sleep: Move runtime PM barrier invocation to device

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Date:	Tue, 13 May 2014 17:19:43 +0200
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Ulf Hansson <ulf.hansson@...aro.org>
Cc:	Alan Stern <stern@...land.harvard.edu>,
	Linux PM list <linux-pm@...r.kernel.org>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	Aaron Lu <aaron.lu@...el.com>,
	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Kevin Hilman <khilman@...aro.org>
Subject: Re: [RFC][PATCH 1/3] PM / sleep: Move runtime PM barrier invocation to device_prepare()

On Tuesday, May 13, 2014 05:07:12 PM Rafael J. Wysocki wrote:
> On Tuesday, May 13, 2014 12:59:43 PM Ulf Hansson wrote:
> > On 13 May 2014 12:35, Rafael J. Wysocki <rjw@...ysocki.net> wrote:
> > > On Tuesday, May 13, 2014 11:16:34 AM Ulf Hansson wrote:
> > >> On 13 May 2014 03:03, Rafael J. Wysocki <rjw@...ysocki.net> wrote:
> > >> > From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> > >> >
> > >> > Move the invocation of the runtime PM barrier during system suspend
> > >> > (or hibernation) from __device_suspend() to device_prepare() to make
> > >> > all runtime PM transitions in progress complete before executing
> > >> > ->prepare() callbacks for devices.
> > >> >
> > >> > That will allow those callbacks to check if devices are runtime
> > >> > suspended in a non-racy way.
> > >> >
> > >> > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> > >> > ---
> > >> >  drivers/base/power/main.c |   31 +++++++++++++------------------
> > >> >  1 file changed, 13 insertions(+), 18 deletions(-)
> > >> >
> > >> > Index: linux-pm/drivers/base/power/main.c
> > >> > ===================================================================
> > >> > --- linux-pm.orig/drivers/base/power/main.c
> > >> > +++ linux-pm/drivers/base/power/main.c
> > >> > @@ -1312,24 +1312,7 @@ static int __device_suspend(struct devic
> > >> >
> > >> >         dpm_wait_for_children(dev, async);
> > >> >
> > >> > -       if (async_error)
> > >> > -               goto Complete;
> > >> > -
> > >> > -       /*
> > >> > -        * If a device configured to wake up the system from sleep states
> > >> > -        * has been suspended at run time and there's a resume request pending
> > >> > -        * for it, this is equivalent to the device signaling wakeup, so the
> > >> > -        * system suspend operation should be aborted.
> > >> > -        */
> > >> > -       if (pm_runtime_barrier(dev) && device_may_wakeup(dev))
> > >> > -               pm_wakeup_event(dev, 0);
> > >> > -
> > >> > -       if (pm_wakeup_pending()) {
> > >> > -               async_error = -EBUSY;
> > >> > -               goto Complete;
> > >> > -       }
> > >>
> > >> I suppose you went a bit too far here!?
> > >>
> > >> We can still have wakeup pending at this point, and thus we should
> > >> bail out, right?
> > >
> > > That pm_wakeup_pending() is part of the barrier handling, so ->
> > >
> > >> > -
> > >> > -       if (dev->power.syscore)
> > >> > +       if (async_error || dev->power.syscore)
> > >> >                 goto Complete;
> > >> >
> > >> >         dpm_watchdog_set(&wd, dev);
> > >> > @@ -1500,6 +1483,18 @@ static int device_prepare(struct device
> > >> >          */
> > >> >         pm_runtime_get_noresume(dev);
> > >> >
> > >> > +       /*
> > >> > +        * If a device configured to wake up the system from sleep states
> > >> > +        * has been suspended at run time and there's a resume request pending
> > >> > +        * for it, this is equivalent to the device signaling wakeup, so the
> > >> > +        * system suspend operation should be aborted.
> > >> > +        */
> > >> > +       if (pm_runtime_barrier(dev) && device_may_wakeup(dev))
> > >> > +               pm_wakeup_event(dev, 0);
> > >> > +
> > >> > +       if (pm_wakeup_pending())
> > >> > +               return -EBUSY;
> > >> > +
> > >
> > > -> it is done here now.
> > >
> > > I don't see why it would be still necessary in __device_suspend().
> > 
> > Can't we have wakeup configured for !CONFIG_PM_RUNTIME case?
> > pm_runtime_barrier() won't handle those scenarios, right?
> 
> The pm_wakeup_pending() is in effect for CONFIG_PM_RUNTIME unset too.
> 
> > Similar check for pm_wakeup_pending() is done at
> > __device_suspend_noirq, __device_suspend_late - I assumed it was
> > because of the same reasons.
> 
> Hmm, OK.  I'll leave it in __device_suspend() too, then.

Well, actually, that wouldn't make much sense in my opinion.

Why would the device status change between device_prepare() and
__device_suspend() if we do the barrier in device_prepare()?


-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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