Re: [PATCH 1/3] mpc52xx/wdt: OF property to enable the WDT on boot

[Grant Likely <grant.likely@secretlab.ca>]

On Tue, Nov 10, 2009 at 12:40 PM, Albrecht Dreß <albrecht.dress@arcor.de> wrote:
> Add the "wdt,on-boot" OF property as to reserve a GPT as WDT which may be a
> requirement in safety-related (e.g. ISO 61508) applications.
>
> Signed-off-by: Albrecht Dreß <albrecht.dress@arcor.de>
> ---
>
>  Documentation/powerpc/dts-bindings/fsl/mpc5200.txt |   15 ++++++++++++++-
>  1 files changed, 14 insertions(+), 1 deletions(-)
>
> diff --git a/Documentation/powerpc/dts-bindings/fsl/mpc5200.txt b/Documentation/powerpc/dts-bindings/fsl/mpc5200.txt
> index 8447fd7..1eecb06 100644
> --- a/Documentation/powerpc/dts-bindings/fsl/mpc5200.txt
> +++ b/Documentation/powerpc/dts-bindings/fsl/mpc5200.txt
> @@ -103,7 +103,20 @@ fsl,mpc5200-gpt nodes
>  ---------------------
>  On the mpc5200 and 5200b, GPT0 has a watchdog timer function.  If the board
>  design supports the internal wdt, then the device node for GPT0 should
> -include the empty property 'fsl,has-wdt'.
> +include the empty property 'fsl,has-wdt'.  Note that this does not activate
> +the watchdog.  The timer will function as a GPT if the timer api is used, and
> +it will function as watchdog if the watchdog device is used.  The watchdog
> +mode has priority over the gpt mode, i.e. if the watchdog is activated, any
> +gpt api call to this timer will fail with -EBUSY.
> +
> +If you add the property
> +       wdt,on-boot = <n>;
> +GPT0 will be marked as in-use watchdog, i.e. blocking every gpt access to it.
> +If n>0, the watchdog is started with a timeout of n seconds.  If n=0, the
> +configuration of the watchdog is not touched.  This is useful in two cases:
> +- just mark GPT0 as watchdog, blocking gpt accesses, and configure it later;
> +- do not touch a configuration assigned by the boot loader which supervises
> +  the boot process itself.

I'm not *totally* convinced on the usage model, but I just need some
time to think about it.  Give me a day or so and ping me again if you
haven't heard from me.  However, until a common WDT binding is
defined, this property needs to be named something like
"fsl,wdt-on-boot".

Cheers,
g.

-- 
Grant Likely, B.Sc., P.Eng.
Secret Lab Technologies Ltd.