linux-kernel - Re: [PATCH 2/3] dt-bindings: watchdog: fsl-imx: document suspend in wait mode

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Date:   Thu, 20 Oct 2022 08:18:26 -0400
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Andrej Picej <andrej.picej@...ik.com>,
        Alexander Stein <alexander.stein@...tq-group.com>
Cc:     linux-watchdog@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, shawnguo@...nel.org,
        linux@...ck-us.net, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org, linux-imx@....com, festevam@...il.com,
        kernel@...gutronix.de, s.hauer@...gutronix.de,
        wim@...ux-watchdog.org, robh+dt@...nel.org
Subject: Re: [PATCH 2/3] dt-bindings: watchdog: fsl-imx: document suspend in
 wait mode

On 20/10/2022 02:23, Andrej Picej wrote:
> Hi Alexander and Krzysztof,
> 
> hope I can reply to both questions here.
> 
> On 19. 10. 22 17:51, Krzysztof Kozlowski wrote:
>> On 19/10/2022 09:00, Alexander Stein wrote:
>>> Hello Andrej,
>>>
>>> Am Mittwoch, 19. Oktober 2022, 13:17:13 CEST schrieb Andrej Picej:
>>
>> Missing commit msg.
>>
>>>> Signed-off-by: Andrej Picej <andrej.picej@...ik.com>
>>>> ---
>>>>   Documentation/devicetree/bindings/watchdog/fsl-imx-wdt.yaml | 5 +++++
>>>>   1 file changed, 5 insertions(+)
>>>>
>>>> diff --git a/Documentation/devicetree/bindings/watchdog/fsl-imx-wdt.yaml
>>>> b/Documentation/devicetree/bindings/watchdog/fsl-imx-wdt.yaml index
>>>> fb7695515be1..01b3e04e7e65 100644
>>>> --- a/Documentation/devicetree/bindings/watchdog/fsl-imx-wdt.yaml
>>>> +++ b/Documentation/devicetree/bindings/watchdog/fsl-imx-wdt.yaml
>>>> @@ -55,6 +55,11 @@ properties:
>>>>         If present, the watchdog device is configured to assert its
>>>>         external reset (WDOG_B) instead of issuing a software reset.
>>>>
>>>> +  fsl,suspend-in-wait:
>>>> +    $ref: /schemas/types.yaml#/definitions/flag
>>>> +    description: |
>>>> +      If present, the watchdog device is suspended in WAIT mode.
>>>> +
>>>>   required:
>>>>     - compatible
>>>>     - interrupts
>>>
>>> What is the condition the watchdog is suspended in WAIT mode? Is this specific
>>> to SoC or platform or something else?
>>>
>>
> 
> Sorry, what exactly do you mean by condition?

Ugh, I also cannot parse it now...

> When the property 
> "fsl,suspend-in-wait" is set the watchdog is suspended in WAIT mode, so 
> this is defined by the user. Didn't want to apply it for all the 
> supported machines since there could be devices which depend on watchdog 
> triggering in WAIT mode. We stumbled on this problem on imx6 devices, 
> but the same bit (with the same description) is found on imx25, imx35, 
> imx50/51/53, imx7 and imx8.

I meant, what is expected to happen if you do not enable this bit and
watchdog triggers in WAIT mode? IOW, why someone might want to enable or
disable this property?

> 
>> And what happens else? When it is not suspended in WAIT mode?
>>
> 
> When you put the device in "freeze"/"Suspend-To-Idle" low-power mode the 
> watchdog keeps running and triggers a reset after 128 seconds. So the 
> maximum length the device can stay in this mode is limited to 128 seconds.

And who wakes up the system before 128 seconds? IOW is there a use case
of not enabling this property?

Best regards,
Krzysztof