linux-kernel - Re: [PATCH v2 5/6] watchdog: at91sam9: request the irq with IRQF_NO

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Date:	Thu, 5 Mar 2015 16:10:16 +0100
From:	"Rafael J. Wysocki" <rafael@...nel.org>
To:	Mark Rutland <mark.rutland@....com>
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Boris Brezillon <boris.brezillon@...e-electrons.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Jason Cooper <jason@...edaemon.net>,
	Peter Zijlstra <peterz@...radead.org>,
	Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	Wim Van Sebroeck <wim@...ana.be>,
	"linux-watchdog@...r.kernel.org" <linux-watchdog@...r.kernel.org>,
	Alessandro Zummo <a.zummo@...ertech.it>,
	"rtc-linux@...glegroups.com" <rtc-linux@...glegroups.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jslaby@...e.cz>,
	"linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
	Mike Turquette <mturquette@...aro.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Nicolas Ferre <nicolas.ferre@...el.com>,
	Jean-Christophe Plagniol-Villard <plagnioj@...osoft.com>,
	Alexandre Belloni <alexandre.belloni@...e-electrons.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v2 5/6] watchdog: at91sam9: request the irq with IRQF_NO_SUSPEND

On Thu, Mar 5, 2015 at 11:57 AM, Mark Rutland <mark.rutland@....com> wrote:
> [...]
>
>> > >           err = request_irq(wdt->irq, wdt_interrupt,
>> > > -                           IRQF_SHARED | IRQF_IRQPOLL,
>> > > +                           IRQF_SHARED | IRQF_IRQPOLL |
>> > > +                           IRQF_NO_SUSPEND,
>> >
>> > I'm a little confused by this. What happens if the watchdog fires when
>> > we're actually in the suspended state (when IRQF_NO_SUSPEND interrupts
>> > aren't guaranteed to be delivered).
>>
>> Why wouldn't they be delivered?
>>
>> If that's suspend-to-idle, we'll handle them normally.  If that's full suspend,
>> they may not be handled at the last stage (when we run on one CPU with interrupts
>> off), but that was the case before the wakeup interrupts rework already and I'd
>> expect it to be taken into account somehow in the existing code (or if it isn't
>> taken into account, we have a bug, but it is not related to this series).
>
> There's no enable_irq_wake(wdt->irq), and I was under the impression this
> is for full suspend.

enable_irq_wake() has no effect on IRQF_NO_SUSPEND interrupts, so if the
driver uses IRQF_NO_SUSPEND, it does not need to use enable_irq_wake()
in addition to that.

Drivers using IRQF_COND_SUSPEND generally should use enable_irq_wake() too
in case they end up in a situation without sharing a NO_SUSPEND interrupt, in
which case their interrupt handlers won't be called after suspend_device_irqs(),
so they need to rely on the core to do the wakeup.

> I agree that if problematic, it's an existing bug. Given Boris's
> comments in the other thread this may just a minor semantic issue w.r.t.
> IRQF_NO_SUSPEND vs IRQF_COND_SUSPEND.

It depends on whether or not the watchdog's interrupt handler has to be
called immediately after receiving an interrupt (IRQF_NO_SUSPEND is
better then) or it can be deferred till the resume_device_irqs() time.

Rafael
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