Re: [PATCH] PM / wakeirq: report wakeup events in dedicated wake-IRQs

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
Date: Fri, 11 Nov 2016 14:29:11 -0800	[thread overview]
Message-ID: <20161111222911.GL7138@atomide.com> (raw)
In-Reply-To: <CAJZ5v0jkwHnCPhdm6XAgiWz2=X1SPbfHVHZtZ-ONsp2OL0d-4w@mail.gmail.com>

* Rafael J. Wysocki <rafael@kernel.org> [161111 13:33]:
> On Fri, Nov 11, 2016 at 5:31 PM, Tony Lindgren <tony@atomide.com> wrote:
> > * 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.
> 
> But we drop the lock in rpm_callback(), so can't it be moved to where
> the callback is invoked?

Then we're back to patching all the drivers again, no?

Tony