[PATCHv2 1/3] mpc52xx/wdt: OF property to enable the WDT on boot

[PATCHv2 1/3] mpc52xx/wdt: OF property to enable the WDT on boot

[Albrecht Dreß]

Add the "fsl,wdt-on-boot" OF property as to reserve a GPT as WDT which may
be a requirement in safety-related (e.g. ISO/EN 61508) applications.

Signed-off-by: Albrecht Dreß <albrecht.dress@arcor.de>

---

Change against v1: rename the new property.

 Documentation/powerpc/dts-bindings/fsl/mpc5200.txt |   17 ++++++++++++++++-
 1 files changed, 16 insertions(+), 1 deletions(-)

diff --git a/Documentation/powerpc/dts-bindings/fsl/mpc5200.txt b/Documentation/powerpc/dts-bindings/fsl/mpc5200.txt
index 8447fd7..ddd5ee3 100644
--- a/Documentation/powerpc/dts-bindings/fsl/mpc5200.txt
+++ b/Documentation/powerpc/dts-bindings/fsl/mpc5200.txt
@@ -103,7 +103,22 @@ 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
+	fsl,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.
+
+The watchdog will respect the CONFIG_WATCHDOG_NOWAYOUT option.
 
 An mpc5200-gpt can be used as a single line GPIO controller.  To do so,
 add the following properties to the gpt node:

Re: [PATCHv2 1/3] mpc52xx/wdt: OF property to enable the WDT on boot

[Grant Likely]

On Thu, Nov 12, 2009 at 11:43 AM, Albrecht Dreß <albrecht.dress@arcor.de> wrote:
> Add the "fsl,wdt-on-boot" OF property as to reserve a GPT as WDT which may
> be a requirement in safety-related (e.g. ISO/EN 61508) applications.
>
> Signed-off-by: Albrecht Dreß <albrecht.dress@arcor.de>
>
> ---
>
> Change against v1: rename the new property.
>
>  Documentation/powerpc/dts-bindings/fsl/mpc5200.txt |   17 ++++++++++++++++-
>  1 files changed, 16 insertions(+), 1 deletions(-)
>
> diff --git a/Documentation/powerpc/dts-bindings/fsl/mpc5200.txt b/Documentation/powerpc/dts-bindings/fsl/mpc5200.txt
> index 8447fd7..ddd5ee3 100644
> --- a/Documentation/powerpc/dts-bindings/fsl/mpc5200.txt
> +++ b/Documentation/powerpc/dts-bindings/fsl/mpc5200.txt
> @@ -103,7 +103,22 @@ 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
> +       fsl,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.
> +
> +The watchdog will respect the CONFIG_WATCHDOG_NOWAYOUT option.

I think it would be better to use a device tree property to enable up
NOWAYOUT.  The static config isn't multiplatform-friendly.  Thoughts?

Otherwise, this looks good to me.

g.

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

Re: [PATCHv2 1/3] mpc52xx/wdt: OF property to enable the WDT on boot

[Albrecht Dreß]

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Hi Grant!

Am 12.11.09 20:06 schrieb(en) Grant Likely:
> > +The watchdog will respect the CONFIG_WATCHDOG_NOWAYOUT option.
> 
> I think it would be better to use a device tree property to enable up
> NOWAYOUT.  The static config isn't multiplatform-friendly.  Thoughts?

I fully agree with you that this property would fit perfectly in the device tree.  However, if we now add it *only* for the 52xx, but not for other device tree-aware platforms, this might be somewhat confusing.  The good thing is that it wouldn't break  
anything for the 5200 as the old wdt driver didn't work anyway.

One *real* advantage of the compile-time option is that it actually removes the code which stops the wdt.  I'm not a real expert in that, but if we argue that the system is "safe" as required by IEC/EN 61508 part 3, it's probably beneficial if we can show  
that there *is* no code to stop the wdt, not a snipplet only disabled by a flag.

Just my €0.01, though - maybe more insight from the WDT gurus?

Cheers, Albrecht.

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