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

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Message-ID: <20150307112932.GA1372@amd>
Date:	Sat, 7 Mar 2015 12:29:33 +0100
From:	Pavel Machek <pavel@....cz>
To:	Alexandre Belloni <alexandre.belloni@...e-electrons.com>
Cc:	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>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	"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

On Sat 2015-03-07 12:06:45, Alexandre Belloni wrote:
> On 07/03/2015 at 11:39:39 +0100, Pavel Machek wrote :
> > > The Atmel watchdog can't be stopped once it's started. This is actually 
> > > very useful so we can reset if suspend or resume failed, the only 
> > > drawback is that you have to wake up from time to time (e.g. by using 
> > > the RTC/RTT) to clear the watchdog and then go back to sleep ASAP.
> > 
> > Yeah. So you do "echo mem > /sys/power/state", and few seconds/minutes
> > after watchdog kills the system. But you did not ask for dead system,
> > you asked for suspend.
> > 
> > And while that behaviour is useful for you, I don't think it is
> > exactly useful behaviour, nor it is the behaviour user would expect.
> > 
> 
> 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.

									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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