[PATCH 1/4] dt-bindings: watchdog: aspeed: Add property for WDT SW reset

[Chin-Ting Kuo]

Hi Krzysztof,

Thanks for the review.

> -----Original Message-----
> From: Krzysztof Kozlowski <krzk at kernel.org>
> Sent: Monday, October 7, 2024 2:58 PM
> Subject: Re: [PATCH 1/4] dt-bindings: watchdog: aspeed: Add property for WDT
> SW reset
> 
> On 07/10/2024 08:34, Chin-Ting Kuo wrote:
> > Add "aspeed,restart-sw" property to distinguish normal WDT reset from
> > system restart triggered by SW consciously.
> >
> > Signed-off-by: Chin-Ting Kuo <chin-ting_kuo at aspeedtech.com>
> > ---
> >  .../bindings/watchdog/aspeed,ast2400-wdt.yaml         | 11
> +++++++++++
> >  1 file changed, 11 insertions(+)
> >
> > diff --git
> > a/Documentation/devicetree/bindings/watchdog/aspeed,ast2400-wdt.yaml
> > b/Documentation/devicetree/bindings/watchdog/aspeed,ast2400-wdt.yaml
> > index be78a9865584..6cc3604c295a 100644
> > ---
> > a/Documentation/devicetree/bindings/watchdog/aspeed,ast2400-wdt.yaml
> > +++ b/Documentation/devicetree/bindings/watchdog/aspeed,ast2400-wdt.ya
> > +++ ml
> > @@ -95,6 +95,17 @@ properties:
> >        array with the first word defined using the AST2600_WDT_RESET1_*
> macros,
> >        and the second word defined using the AST2600_WDT_RESET2_*
> macros.
> >
> > +  aspeed,restart-sw:
> > +    $ref: /schemas/types.yaml#/definitions/flag
> > +    description: >
> 
> Why >?
> 

">" will be removed in the next patch series and the description content will be
concatenated after the colon, ":".

> > +      Normally, ASPEED WDT reset may occur when system hangs or
> reboot
> > +      triggered by SW consciously. However, system doesn't know whether
> the
> > +      restart is triggered by SW consciously since the reset event flag is
> > +      the same as normal WDT timeout reset. With this property, SW
> > + can
> 
> So DTS has this property and watchdog bites (timeout) but you will ignore it
> and claim that it was software choice?
> 

No. Normally, when WDT is enabled, a counter is also be enabled. When the counter
is equal to an expected value, timeout event occurs. AST2600 hardware supports a SW
mode, when a magic number is filled into a specific register, WDT reset is triggered
immediately without controlling the counter and the counter is not counted.
Thus, WDT timeout doesn't occur.

> This does not make much sense to me, at least based on this explanation
> 
> > +      restart the system immediately and directly without wait for WDT
> > +      timeout occurs. The reset event flag is also different from the
> normal
> > +      WDT reset. This property is only supported since AST2600 platform.
> 
> Supported as drivers? How is this related? Or you mean hardware? Then
> property should be restricted there.
> 

It is a hardware supported function on AST2600. For platform compatibility, without
this property, all behaviors are the same as the previous generation platform, AST2500.

This property may be removed in the next patch series with referring to Rob suggestion
in the other reply. After checking with the major users, it is feasible to remove this
property and using SW reset by default when the restart operation is triggered by SW
deliberately on AST2600 platform.

> Best regards,
> Krzysztof

Best Wishes,
Chin-Ting