Subject: [PATCH] at91sam9_wdt: Allow watchdog to reset device at early boot

From: [email-masked] (Boris Brezillon)
Date: Thu, 27 Nov 2014 20:00:36 +0100

Hi Timo,

Sorry for the late reply.

On Fri, 21 Nov 2014 14:23:30 +0200
Timo Kokkonen <[email-masked]> 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
> "enable-early-reset" which will prevent the kernel timer from pinging
> the watchdog HW on behalf of user space. 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 <[email-masked]>
> ---
>  Documentation/devicetree/bindings/watchdog/atmel-wdt.txt | 4 ++++
>  drivers/watchdog/at91sam9_wdt.c                          | 6 +++++-
>  2 files changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/devicetree/bindings/watchdog/atmel-wdt.txt b/Documentation/devicetree/bindings/watchdog/atmel-wdt.txt
> index f90e294..a0b7b75 100644
> --- a/Documentation/devicetree/bindings/watchdog/atmel-wdt.txt
> +++ b/Documentation/devicetree/bindings/watchdog/atmel-wdt.txt
> @@ -28,6 +28,10 @@ Optional properties:
>  	entering idle state.
>  - atmel,dbg-halt : Should be present if you want to stop the watchdog when
>  	entering debug state.
> +- enable-early-reset : Should be present if you want to let the
> +	watchdog timer to expire even before user space has opened the
> +	device. If not set, a kernel timer will keep on pinging the
> +	watchdog until it is opened.

If you want to make this property generic, maybe you should document it
in a generic binding doc
(Documentation/devicetree/bindings/watchdog/watchdog.txt ?).
Once you're at it, maybe you could document the generic timeout-sec
property in this file.
Moreover, you might want to parse this property in watchdog_core.c and
store the information in the watchdog_device struct.

Apart from that, I'm not opposed to the approach, and I'm fine with the
current implementation.

Regards,

Boris

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