Re: [PATCH 2/2] at91sam9_wdt: Allow watchdog to reset device at early boot

[Boris Brezillon <boris.brezillon@free-electrons.com>]

Hi Timo,

On Wed, 18 Feb 2015 14:57:22 +0200
Timo Kokkonen <timo.kokkonen@offcode.fi> wrote:

> By default the driver will start a kernel timer which keeps on kicking
> the watchdog HW until user space has opened the watchdog
> device. Usually this is desirable as the watchdog HW is running by
> default and the user space may not have any watchdog daemon running at
> all.
> 
> However, on production systems it may be mandatory that also early
> crashes and lockups will lead to a watchdog reset, even if they happen
> before the user space has opened the watchdog device.
> 
> To resolve the issue, add a new device tree property
> "early-timeout-sec" which will let the kernel timer to ping the
> watchdog HW only as long as the specified timeout permits. The default
> is still to use kernel timer, but more strict behavior can be enabled
> via the device tree property.
> 
> Signed-off-by: Timo Kokkonen <timo.kokkonen@offcode.fi>
> ---
>  Documentation/devicetree/bindings/watchdog/watchdog.txt | 7 +++++++
>  drivers/watchdog/at91sam9_wdt.c                         | 9 ++++++++-
>  2 files changed, 15 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/devicetree/bindings/watchdog/watchdog.txt b/Documentation/devicetree/bindings/watchdog/watchdog.txt
> index 7e3686c..32647cf 100644
> --- a/Documentation/devicetree/bindings/watchdog/watchdog.txt
> +++ b/Documentation/devicetree/bindings/watchdog/watchdog.txt
> @@ -4,9 +4,16 @@ using these definitions.
>  
>  Optional properties:
>  - timeout-sec: Contains the watchdog timeout in seconds.
> +- early-timeout-sec: If present, specifies a timeout value in seconds
> +  that the driver keeps on ticking the watchdog HW on behalf of user
> +  space. Once this timeout expires watchdog is left to expire in
> +  timeout-sec seconds. If this propery is set to zero, watchdog is
> +  started (or left running) so that a reset occurs in timeout-sec
> +  since the watchdog was started.
>  
>  Example:
>  
>  watchdog {
>  	 timeout-sec = <60>;
> +	 early-timeout-sec = <120>;
>  };

IMHO the documentation update should be self-contained (it should be
done in a separate patch).

Best Regards,

Boris

-- 
Boris Brezillon, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com