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

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Date:	Mon, 9 Mar 2015 08:55:46 +0100
From:	Alexandre Belloni <alexandre.belloni@...e-electrons.com>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:	Pavel Machek <pavel@....cz>,
	Sylvain Rochet <gradator@...dator.net>,
	Peter Zijlstra <peterz@...radead.org>,
	Mark Rutland <mark.rutland@....com>,
	Boris Brezillon <boris.brezillon@...e-electrons.com>,
	Alessandro Zummo <a.zummo@...ertech.it>,
	Mike Turquette <mturquette@...aro.org>,
	Jason Cooper <jason@...edaemon.net>,
	"rtc-linux@...glegroups.com" <rtc-linux@...glegroups.com>,
	Len Brown <len.brown@...el.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Nicolas Ferre <nicolas.ferre@...el.com>,
	Wim Van Sebroeck <wim@...ana.be>,
	"linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
	Jean-Christophe Plagniol-Villard <plagnioj@...osoft.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Jiri Slaby <jslaby@...e.cz>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-watchdog@...r.kernel.org" <linux-watchdog@...r.kernel.org>
Subject: Re: [PATCH v2 5/6] watchdog: at91sam9: request the irq with
 IRQF_NO_SUSPEND

Hi,

On 08/03/2015 at 02:12:53 +0100, Rafael J. Wysocki wrote :
> > > I think you misunderstood, that is exactly the expected behaviour. This
> > > is hardware defined. Once the watchdog is started, nobody can stop it.
> > > Trying to change the mode register will result in a reset of the
> > > SoC.
> > 
> > Well, it boils down to "what is stronger". Desire to suspend the
> > system, or desire to reboot the system.
> > 
> > It is "echo mem > state", not "echo reboot > state".
> > 
> > > It is documented in the datasheet and any user wanting another behaviour
> > > is out of luck.
> > 
> > Actaully, your platform should just refuse to enter suspend-to-RAM
> > when hw watchdog is enabled.
> 
> Quite likely, depending on how exactly the suspend is implemented.
>

We've had absolutely zero complain on that. It is quite clear in the
datasheet that failing to refresh the watchdog once started will lead to
a reset and that it is impossible to stop.
It is actually quite convenient to also ensure that you can actually
wake up from suspend because that can obviously go wrong.

-- 
Alexandre Belloni, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com
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