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

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Date:   Fri, 11 Nov 2016 16:19:17 -0800
From:   Tony Lindgren <tony@...mide.com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     Brian Norris <briannorris@...omium.org>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Pavel Machek <pavel@....cz>, Len Brown <len.brown@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Brian Norris <computersforpeace@...il.com>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>
Subject: Re: [PATCH] PM / wakeirq: report wakeup events in dedicated wake-IRQs

* Rafael J. Wysocki <rafael@...nel.org> [161111 15:35]:
> On Fri, Nov 11, 2016 at 11:32 PM, Tony Lindgren <tony@...mide.com> wrote:
> > * Tony Lindgren <tony@...mide.com> [161111 14:29]:
> >> * Rafael J. Wysocki <rafael@...nel.org> [161111 13:33]:
> >> > On Fri, Nov 11, 2016 at 5:31 PM, Tony Lindgren <tony@...mide.com> wrote:
> >> > > * Rafael J. Wysocki <rafael@...nel.org> [161110 16:06]:
> >> > >> On Thu, Nov 10, 2016 at 7:49 PM, Brian Norris <briannorris@...omium.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@...omium.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?
> >
> > Sorry I misunderstood, yeah that should work if rpm_callback() drops
> > the lock.
> 
> It still will not re-enable interrupts if the irq_safe flag is set.  I
> wonder if we really care about this case, though.

We have at least 8250-omap and serial-omap using wakeirqs with
irq_safe flag set.

Regards,

Tony