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

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Date:   Fri, 11 Nov 2016 01:06:09 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Brian Norris <briannorris@...omium.org>
Cc:     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>,
        Tony Lindgren <tony@...mide.com>
Subject: Re: [PATCH] PM / wakeirq: report wakeup events in dedicated wake-IRQs

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?

Thanks,
Rafael