Message-ID: <493b1bac-2eae-4c78-9c07-801eaf954b04@gehealthcare.com>
Date: Thu, 8 Jan 2026 09:58:19 +0200
From: Nandor Han <nandor.han@...ealthcare.com>
To: Krzysztof Kozlowski <krzk@...nel.org>
Cc: wim@...ux-watchdog.org, linux@...ck-us.net, robh@...nel.org,
 krzk+dt@...nel.org, conor+dt@...nel.org, shawnguo@...nel.org,
 s.hauer@...gutronix.de, kernel@...gutronix.de, festevam@...il.com,
 linux-watchdog@...r.kernel.org, devicetree@...r.kernel.org,
 imx@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] dt-bindings: watchdog: fsl-imx: document continue in
 low power mode


On 1/7/26 12:48, Krzysztof Kozlowski wrote:
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> On 07/01/2026 10:12, Nandor Han wrote:
>> On 12/30/25 14:34, Krzysztof Kozlowski wrote:
>>> CAUTION: This email originated from outside of GE HealthCare. Only open links or attachments if you trust the sender. Report suspicious emails using Outlook’s “Report” button.
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>>> On Mon, Dec 29, 2025 at 04:50:00PM +0200, Nandor Han wrote:
>>>> Property "fsl,wdt-continue-in-low-power" allows the watchdog to continue
>>>> running in low power modes (STOP and DOZE). By default, the watchdog is
>>>> suspended in these modes. This property provides the option to keep the
>>>> watchdog active during low power states when needed.
>>> And why exactly would that be a DT property? If system is sleeping
>>> (assuming this is what you meant by low power), no one will pet the dog,
>>> thus watchdog makes no sense.
>> Thanks for the feedback Krzysztof and Guenter.
>>
>> In our case, low-power mode is disabled. However, we have identified that under certain conditions,
> If your system has low power mode disabled, then you do not need this
> property - you already know that watchdog must continue (or whatever you
> want to achieve here).
>
>> specifically during simulated high-load scenarios, the device becomes unresponsive because it enters
>> one of these power states.
> Device as watchdog? I really do not understand your explanations, but
> for sure system load is not relevant to DT property.
>
>>> Otherwise I fail to see how this is a hardware property and we do not
>>> accept SW properties (see writing bindings, numerous presentations).
>> Our system is based on the i.MX7D CPU and the watchdog peripheral supports the configuration:
>>
>> (From i.MX 7Dual Applications Processor Reference Manual, Rev. 1, 01/2018, page: 1174)
>> ---
>> WDZST
>> Watchdog Low Power. Determines the operation of the WDOG during low-power modes. This bit is write
>> once-only.
>> ---
>> Given that our system does not support low-power modes, we intend to enable the watchdog across all power
>> states to ensure the device can recover properly under these conditions.
> That's not what your property said. Your property said watchdog should
> continue in low power modes. So when system enters low power mode, how
> the watchdog petting would work?
>
> Now you claim you want to enable it in low power mode but you do not
> have low power mode? Does not make sense to me at all.
>
> Best regards,
> Krzysztof
>
Sorry if anything is unclear. I would try to explain the change from the driver's point of view.

According to i.MX7D Reference Manual, the watchdog controller allows, via the WDOGx_WCR register, control over whether the watchdog continues or suspends in:

a)WAIT power state (bit 7: WDW)
b)STOP and DOSE power state(bit 0: WDZST).

The current driver implementation provides a Device Tree binding `fsl,suspend-in-wait` for configuring case (a) and forces the watchdog to be suspended in case (b).

My patch adds the ability to configure case (b) as well.

Regards,
Nandor

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