linux-kernel - Re: [PATCH 0/8] watchdog: Add support for keepalives triggered by infrastructure

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Message-ID: <20150805073605.GW9999@pengutronix.de>
Date:	Wed, 5 Aug 2015 09:36:05 +0200
From:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>
To:	Pádraig Brady <P@...igBrady.com>
Cc:	Guenter Roeck <linux@...ck-us.net>, linux-watchdog@...r.kernel.org,
	Wim Van Sebroeck <wim@...ana.be>,
	linux-kernel@...r.kernel.org,
	Timo Kokkonen <timo.kokkonen@...code.fi>,
	linux-doc@...r.kernel.org, Jonathan Corbet <corbet@....net>
Subject: Re: [PATCH 0/8] watchdog: Add support for keepalives triggered by
 infrastructure

Hello Pádraig,

On Wed, Aug 05, 2015 at 12:43:39AM +0100, Pádraig Brady wrote:
> On 04/08/15 03:13, Guenter Roeck wrote:
> > The watchdog infrastructure is currently purely passive, meaning
> > it only passes information from user space to drivers and vice versa.
> > 
> > Since watchdog hardware tends to have its own quirks, this can result
> > in quite complex watchdog drivers. A number of scanarios are especially common.
> > 
> > - A watchdog is always active and can not be disabled, or can not be disabled
> >   once enabled. To support such hardware, watchdog drivers have to implement
> >   their own timers and use those timers to trigger watchdog keepalives while
> >   the watchdog device is not or not yet opened.
> > - A variant of this is the desire to enable a watchdog as soon as its driver
> >   has been instantiated, to protect the system while it is still booting up,
> >   but the watchdog daemon is not yet running.
> 
> Just mentioning that patting the watchdog in the boot loader
> (by patching grub etc.) can be a more general solution here as it
> avoids hangs if the kernel crashes before it runs the watchdog driver,
> which is especially true if PXE loaded across the net for example.
> Also this tends to be better spaced between boot start and user space loading.

the watchdog I'm currently working with on a powerpc platform has a
unchangable timeout of ~1 s. To make the machine boot I patched the
bootloader and need some automatic pinging in the kernel before
userspace takes over.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |
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