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

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Message-ID: <20161110184910.GA135921@google.com>
Date:   Thu, 10 Nov 2016 10:49:10 -0800
From:   Brian Norris <briannorris@...omium.org>
To:     Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:     "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 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.