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

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Date:	Sat, 7 Mar 2015 11:39:39 +0100
From:	Pavel Machek <pavel@....cz>
To:	Sylvain Rochet <gradator@...dator.net>
Cc:	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>,
	Alexandre Belloni <alexandre.belloni@...e-electrons.com>,
	"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 11:20:56, Sylvain Rochet wrote:
> Hello,
> 
> On Sat, Mar 07, 2015 at 10:18:46AM +0100, Peter Zijlstra wrote:
> > On Thu, Mar 05, 2015 at 11:53:08AM +0000, Mark Rutland wrote:
> > > If everyone else is happy with this using IRQF_NO_SUSPEND for now then
> > > don't let my comments above block this patch.
> > 
> > Yeah, I'm really not happy with NO_SUSPEND + enable_irq_wake().
> > 
> > I really want that combo to BUG/WARN -- esp. since there's so much cargo
> > culted crap out there.
> > 
> > We should make robust interfaces, not randomly toggle flags until it
> > mostly works by accident rather than by design -- which is what this
> > feels like.
> > 
> > And while I appreciate the watchdog use-case; I think the easiest
> > solution for now is to simply disable the wathdog over suspend until
> > we've come up with something that makes sense.
> > 
> > As it is, you need to 'suspend' the watchdog at some point anyhow; you
> > don't want that thing to wake you from whatever suspend state you're in.
> 
> 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.

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