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

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Date:	Sun, 08 Mar 2015 02:12:53 +0100
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Pavel Machek <pavel@....cz>
Cc:	Alexandre Belloni <alexandre.belloni@...e-electrons.com>,
	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

On Saturday, March 07, 2015 12:29:33 PM Pavel Machek wrote:
> 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.

Quite likely, depending on how exactly the suspend is implemented.


-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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