linux-kernel - Re: [PATCH v4 1/2] watchdog: New watchdog driver for MEN A21 watchdogs

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Message-ID: <20130530215928.GL14258@spo001.leaseweb.com>
Date:	Thu, 30 May 2013 23:59:28 +0200
From:	Wim Van Sebroeck <wim@...ana.be>
To:	Guenter Roeck <linux@...ck-us.net>
Cc:	Johannes Thumshirn <johannes.thumshirn@....de>,
	linux-watchdog@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 1/2] watchdog: New watchdog driver for MEN A21 watchdogs

Hi Guenter,

> On Tue, May 28, 2013 at 10:10:53AM +0200, Johannes Thumshirn wrote:
> > On Mon, May 27, 2013 at 08:25:54PM +0200, Wim Van Sebroeck wrote:
> > [...]
> > > > +	watchdog_set_drvdata(&a21_wdt, drv);
> > >
> > > I am missing the initialisation of the watchdog's timeout value here...
> > 
> > This watchdog only knows two timeout values, 1s and 30s with the constraint
> > that you can't go back to 30s once your in a 1s timeout without a reset of the
> > CPLD. I could initially set it to 30s but that would be redundant.
> > 
> I wonder - why bother with supporting one-second timeouts ?
> 
> Is this realistic, ie can you guarantee that the watchdog will be pinged fast
> enough to keep the system alive under all load conditions ? As far as I know
> you can not even configure the watchdog application for less than 1 second
> ping intervals.

that's why certain drivers use a timer to keep kicking the watchdog at
a rate of 0.5s (do a grep on HZ/2) untill userspace times out.
(example: drivers/watchdog/pika_wdt.c or drivers/watchdog/pcwd.c).

Kind regards,
Wim.

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