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

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Date:	Thu, 5 Mar 2015 09:53:06 +0100
From:	Boris Brezillon <boris.brezillon@...e-electrons.com>
To:	Mark Rutland <mark.rutland@....com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Jason Cooper <jason@...edaemon.net>,
	Peter Zijlstra <peterz@...radead.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	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

Hi Mark,

On Wed, 4 Mar 2015 18:38:09 +0000
Mark Rutland <mark.rutland@....com> wrote:

> Hi Boris,
> 
> On Mon, Mar 02, 2015 at 09:18:17AM +0000, Boris Brezillon wrote:
> > The watchdog interrupt (only used when activating software watchdog)
> > shouldn't be suspended when entering suspend mode, because it is shared
> > with a timer device (which request the line with IRQF_NO_SUSPEND) and once
> > the watchdog "Mode Register" has been written, it cannot be changed (which
> > means we cannot disable the watchdog interrupt when entering suspend).
> > 
> > Signed-off-by: Boris Brezillon <boris.brezillon@...e-electrons.com>
> > ---
> >  drivers/watchdog/at91sam9_wdt.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/watchdog/at91sam9_wdt.c b/drivers/watchdog/at91sam9_wdt.c
> > index 6df9405..1443b3c 100644
> > --- a/drivers/watchdog/at91sam9_wdt.c
> > +++ b/drivers/watchdog/at91sam9_wdt.c
> > @@ -208,7 +208,8 @@ static int at91_wdt_init(struct platform_device *pdev, struct at91wdt *wdt)
> >  
> >  	if ((tmp & AT91_WDT_WDFIEN) && wdt->irq) {
> >  		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).

It reboot the system.

> 
> Does this rely on the watchdog IRQ being taken while in the actual
> suspended state (but not waking up the system while handling it)?

Actually this interrupt handler is just here to reboot the system if the
user didn't refresh the watchdog.
Do we really have to wake up the system to then call emergency_restart ?


-- 
Boris Brezillon, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com
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