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

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Message-ID: <55C1C041.3080504@roeck-us.net>
Date:	Wed, 05 Aug 2015 00:50:25 -0700
From:	Guenter Roeck <linux@...ck-us.net>
To:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>,
	Pádraig Brady <P@...igBrady.com>
CC:	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

Hi Uwe,

On 08/05/2015 12:36 AM, Uwe Kleine-König wrote:
> 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.
>

Does using arch_initcall in the watchdog driver help here, or is that
still too slow and you really need to hack the kernel ?

Thanks,
Guenter

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