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Date: Fri, 11 Nov 2016 08:31:48 -0800
From: Tony Lindgren <tony@atomide.com>
To: "Rafael J. Wysocki" <rafael@kernel.org>
Cc: Brian Norris <briannorris@chromium.org>,
        Dmitry Torokhov <dmitry.torokhov@gmail.com>,
        "Rafael J . Wysocki" <rjw@rjwysocki.net>, Pavel Machek <pavel@ucw.cz>,
        Len Brown <len.brown@intel.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        lkml <linux-kernel@vger.kernel.org>,
        Brian Norris <computersforpeace@gmail.com>,
        "linux-pm@vger.kernel.org" <linux-pm@vger.kernel.org>
Subject: Re: [PATCH] PM / wakeirq: report wakeup events in dedicated wake-IRQs
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* Rafael J. Wysocki <rafael@kernel.org> [161110 16:06]:
> On Thu, Nov 10, 2016 at 7:49 PM, Brian Norris <briannorris@chromium.org> wrote:
> > On Thu, Nov 10, 2016 at 10:13:55AM -0800, Dmitry Torokhov wrote:
> >> On Thu, Nov 10, 2016 at 10:07 AM, Brian Norris <briannorris@chromium.org> wrote:
> >> > It's important that user space can figure out what device woke the
> >> > system from suspend -- e.g., for debugging, or for implementing
> >> > conditional wake behavior. Dedicated wakeup IRQs don't currently do
> >> > that.
> >> >
> >> > Let's report the event (pm_wakeup_event()) and also allow drivers to
> >> > synchronize with these events in their resume path (hence, disable_irq()
> >> > instead of disable_irq_nosync()).
> >>
> >> Hmm, dev_pm_disable_wake_irq() is called from
> >> rpm_suspend()/rpm_resume() that take dev->power.lock spinlock and
> >> disable interrupts. Dropping _nosync() feels dangerous.
> >
> > Indeed. So how do you suggest we get sane wakeup reports? Every device
> > or bus that's going to use the dedicated wake APIs has to
> > synchronize_irq() [1] in their resume() routine? Seems like an odd
> > implementation detail to have to remember (and therefore most drivers
> > will get it wrong).
> >
> > Brian
> >
> > [1] Or maybe at least create a helper API that will extract the
> > dedicated wake IRQ number and do the synchronize_irq() for us, so
> > drivers don't have to stash this separately (or poke at
> > dev->power.wakeirq->irq) for no good reason.
> 
> Well, in the first place, can anyone please refresh my memory on why
> it is necessary to call dev_pm_disable_wake_irq() under power.lock?

I guess no other reason except we need to manage the wakeirq
for rpm_callback(). So we dev_pm_enable_wake_irq() before
rpm_callback() in rpm_suspend(), then disable on resume.

Regards,

Tony