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

[Krzysztof Kozlowski <krzk@kernel.org>]

On 14/10/2024 04:07, Chin-Ting Kuo wrote:
> Hi Krzysztof,
> 
> Thanks for the review.
> 
>> -----Original Message-----
>> From: Krzysztof Kozlowski <krzk@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@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.

How is this a no?

> 
>> 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

s/may/will/

> 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