linux-kernel - Re: [PATCH RFC] watchdog: add a new driver for VIA chipsets

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Date:	Thu, 24 Nov 2011 14:42:47 +0100
From:	Wim Van Sebroeck <wim@...ana.be>
To:	Marc Vertes <marc.vertes@...fox.com>
Cc:	w.sang@...gutronix.de, linux-watchdog@...r.kernel.org,
	linux-kernel@...r.kernel.org, HaraldWelte@...tech.com,
	broonie@...nsource.wolfsonmicro.com
Subject: Re: [PATCH RFC] watchdog: add a new driver for VIA chipsets

Hi Marc,

> I have tested your version and it works fine. I saw that you enforced
> the NO_WAY_OUT bit and implemented the KEEPALIVEPING and MAGICCLOSE
> features properly. Many thanks.

No problem.

> Regarding the timer, the driver can not read the timeout value set in
> the BIOS, so there is still a risk of reboot if the BIOS value is lower
> than driver one. I assume that other drivers may be in the same case,
> and that is required for user compatibility anyway.

The driver assumes 1 second as heartbeat of the watchdog device.
It thus takes half of this time do actually 'tickle' the watchdog. (or 500ms).
We should set this 1 second value to the smallest time that is possible (either
the smallest value that can be set in the BIOS or the smallest value that is
listed in the datasheets).

> Here is the comment block that I propose to insert regarding register
> programming issues:
> 
> /*
>  * Caveat: the only known way to activate the watchdog timer or to set
>  * its period is through BIOS configuration, when the hardware supports it.
>  * It seems that the watchdog control registers are locked and disabled if
>  * the watchdog is not exposed or enabled by BIOS, and that writing them is
>  * useless. No public documentation is available regarding this limitation.
>  */

Looks good. I will add this. Just let me know what the smallest value is for
the timeout in the BIOS and/or datasheet and I will do the necessary for inclusion
in the watchdog tree.

Kind regards,
Wim.

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