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

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Message-ID: <CAK7N6vpwizg3zAJtY2VTsXoccPhsAx0B5Em4TSJoRycz421S3Q@mail.gmail.com>
Date:	Fri, 31 May 2013 15:05:50 +0530
From:	anish singh <anish198519851985@...il.com>
To:	Guenter Roeck <linux@...ck-us.net>
Cc:	Wim Van Sebroeck <wim@...ana.be>,
	Johannes Thumshirn <johannes.thumshirn@....de>,
	linux-watchdog@...r.kernel.org,
	linux-kernel-mail <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 1/2] watchdog: New watchdog driver for MEN A21 watchdogs

Hi Guenter,

On Fri, May 31, 2013 at 3:32 AM, Guenter Roeck <linux@...ck-us.net> wrote:
> On Thu, May 30, 2013 at 11:59:28PM +0200, Wim Van Sebroeck wrote:
>> 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).
>>
> Yes, I have used the same trick in a couple of my drivers. That isn't done here,
> though.
>
> I even thought about adding this capability to the infrastructure.

If you don't mind can I give it a try?
>
> Thanks,
> Guenter
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