[PATCH 0/2] watchdog: imx2_wdt: Allow to run in low power mode

[PATCH 0/2] watchdog: imx2_wdt: Allow to run in low power mode

[Nandor Han]

Description
-----------
Add the possibility for the user to allow the configuration of watchdog
in low power mode.

Testing
-------
It was verified on a i.MX7D based system that once enabled the watchdog
will reset the device when the system enter in low power mode.

Nandor Han (2):
  watchdog: imx2_wdt: Allow to continue in low power mode
  dt-bindings: watchdog: fsl-imx: document continue in low power mode

 .../devicetree/bindings/watchdog/fsl-imx-wdt.yaml          | 6 ++++++
 drivers/watchdog/imx2_wdt.c                                | 7 ++++++-
 2 files changed, 12 insertions(+), 1 deletion(-)

-- 
2.39.5

[PATCH 1/2] watchdog: imx2_wdt: Allow to continue in low power mode

[Nandor Han]

By default, the driver suspends the watchdog in low power modes (STOP
and DOZE). In some situations this is not desired.

Add the possibility to configure the continuation of the watchdog timer
in the above mentioned low power modes.

Note:
Please be advised that the difference between the variable name and the
device tree option has been intentionally selected to uphold the
prevailing driver functionality. This ensures that the watchdog remains
suspended by default in low power mode, while also facilitating a clear
and intelligible device tree option name.

Signed-off-by: Nandor Han <nandor.han@gehealthcare.com>
---
 drivers/watchdog/imx2_wdt.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/watchdog/imx2_wdt.c b/drivers/watchdog/imx2_wdt.c
index 4b3a192ee3e8..6e837cfc3c5a 100644
--- a/drivers/watchdog/imx2_wdt.c
+++ b/drivers/watchdog/imx2_wdt.c
@@ -71,6 +71,7 @@ struct imx2_wdt_device {
 	struct watchdog_device wdog;
 	const struct imx2_wdt_data *data;
 	bool ext_reset;
+	bool wdt_suspend_in_low_power;
 	bool clk_is_on;
 	bool no_ping;
 	bool sleep_wait;
@@ -135,7 +136,8 @@ static inline void imx2_wdt_setup(struct watchdog_device *wdog)
 	regmap_read(wdev->regmap, IMX2_WDT_WCR, &val);
 
 	/* Suspend timer in low power mode, write once-only */
-	val |= IMX2_WDT_WCR_WDZST;
+	if (wdev->wdt_suspend_in_low_power)
+		val |= IMX2_WDT_WCR_WDZST;
 	/* Suspend timer in low power WAIT mode, write once-only */
 	if (wdev->sleep_wait)
 		val |= IMX2_WDT_WCR_WDW;
@@ -326,6 +328,9 @@ static int __init imx2_wdt_probe(struct platform_device *pdev)
 	wdev->ext_reset = of_property_read_bool(dev->of_node,
 						"fsl,ext-reset-output");
 
+	wdev->wdt_suspend_in_low_power = !of_property_read_bool(dev->of_node,
+						"fsl,wdt-continue-in-low-power");
+
 	if (of_property_read_bool(dev->of_node, "fsl,suspend-in-wait")) {
 		if (!wdev->data->wdw_supported) {
 			dev_err(dev, "suspend-in-wait not supported\n");
-- 
2.39.5

[PATCH 2/2] dt-bindings: watchdog: fsl-imx: document continue in low power mode

[Nandor Han]

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.

Signed-off-by: Nandor Han <nandor.han@gehealthcare.com>
---
 Documentation/devicetree/bindings/watchdog/fsl-imx-wdt.yaml | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/Documentation/devicetree/bindings/watchdog/fsl-imx-wdt.yaml b/Documentation/devicetree/bindings/watchdog/fsl-imx-wdt.yaml
index 34951783a633..4dd9cc81c926 100644
--- a/Documentation/devicetree/bindings/watchdog/fsl-imx-wdt.yaml
+++ b/Documentation/devicetree/bindings/watchdog/fsl-imx-wdt.yaml
@@ -64,6 +64,12 @@ properties:
       If present, the watchdog device is suspended in WAIT mode
       (Suspend-to-Idle). Only supported on certain devices.
 
+  fsl,wdt-continue-in-low-power:
+    $ref: /schemas/types.yaml#/definitions/flag
+    description: |
+      If present, the watchdog device continues to run in low power modes
+      (STOP and DOZE). By default, the watchdog is suspended in these modes.
+
 required:
   - compatible
   - interrupts
-- 
2.39.5

Re: [PATCH 2/2] dt-bindings: watchdog: fsl-imx: document continue in low power mode

[Krzysztof Kozlowski]

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.

Otherwise I fail to see how this is a hardware property and we do not
accept SW properties (see writing bindings, numerous presentations).

Best regards,
Krzysztof

Re: [PATCH 1/2] watchdog: imx2_wdt: Allow to continue in low power mode

[Krzysztof Kozlowski]

On Mon, Dec 29, 2025 at 04:49:59PM +0200, Nandor Han wrote:
> By default, the driver suspends the watchdog in low power modes (STOP
> and DOZE). In some situations this is not desired.
> 
> Add the possibility to configure the continuation of the watchdog timer
> in the above mentioned low power modes.
> 
> Note:
> Please be advised that the difference between the variable name and the
> device tree option has been intentionally selected to uphold the
> prevailing driver functionality. This ensures that the watchdog remains
> suspended by default in low power mode, while also facilitating a clear
> and intelligible device tree option name.
>

Please organize the patch documenting the compatible (DT bindings)
before the patch using that compatible.
See also: https://elixir.bootlin.com/linux/v6.14-rc6/source/Documentation/devicetree/bindings/submitting-patches.rst#L46

Best regards,
Krzysztof

Re: [PATCH 1/2] watchdog: imx2_wdt: Allow to continue in low power mode

[Guenter Roeck]

On Mon, Dec 29, 2025 at 04:49:59PM +0200, Nandor Han wrote:
> By default, the driver suspends the watchdog in low power modes (STOP
> and DOZE). In some situations this is not desired.

Following up on Krzysztof's comment to the devicetree patch:
Assuming the watchdog is in low power mode while the system is
suspended, it is all but impossible to imagine what those situations
might be. A reset by watchdog after the system is suspended simply
does not make sense. A system which must not go into suspend mode
must not be permitted to go into suspend mode to start with, or in
other words suspend mode must not be enabled to start with on such
systems.

Guenter

Re: [PATCH 2/2] dt-bindings: watchdog: fsl-imx: document continue in low power mode

[Peng Fan]

Hi Nandor,

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.

From the cover letter, I see that system should reset if runs into
low power mode. So your system are not allowed to run into low power mode.

If my understanding is correct, DT property should not be used.
You may need to use sysfs or module_parameter for your case.

Regards,
Peng

>
>Signed-off-by: Nandor Han <nandor.han@gehealthcare.com>
>---
> Documentation/devicetree/bindings/watchdog/fsl-imx-wdt.yaml | 6 ++++++
> 1 file changed, 6 insertions(+)
>
>diff --git a/Documentation/devicetree/bindings/watchdog/fsl-imx-wdt.yaml b/Documentation/devicetree/bindings/watchdog/fsl-imx-wdt.yaml
>index 34951783a633..4dd9cc81c926 100644
>--- a/Documentation/devicetree/bindings/watchdog/fsl-imx-wdt.yaml
>+++ b/Documentation/devicetree/bindings/watchdog/fsl-imx-wdt.yaml
>@@ -64,6 +64,12 @@ properties:
>       If present, the watchdog device is suspended in WAIT mode
>       (Suspend-to-Idle). Only supported on certain devices.
> 
>+  fsl,wdt-continue-in-low-power:
>+    $ref: /schemas/types.yaml#/definitions/flag
>+    description: |
>+      If present, the watchdog device continues to run in low power modes
>+      (STOP and DOZE). By default, the watchdog is suspended in these modes.
>+
> required:
>   - compatible
>   - interrupts
>-- 
>2.39.5
>

Re: [PATCH 1/2] watchdog: imx2_wdt: Allow to continue in low power mode

[Nandor Han]

On 12/30/25 14:35, 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.
>
> On Mon, Dec 29, 2025 at 04:49:59PM +0200, Nandor Han wrote:
>> By default, the driver suspends the watchdog in low power modes (STOP
>> and DOZE). In some situations this is not desired.
>>
>> Add the possibility to configure the continuation of the watchdog timer
>> in the above mentioned low power modes.
>>
>> Note:
>> Please be advised that the difference between the variable name and the
>> device tree option has been intentionally selected to uphold the
>> prevailing driver functionality. This ensures that the watchdog remains
>> suspended by default in low power mode, while also facilitating a clear
>> and intelligible device tree option name.
>>
> Please organize the patch documenting the compatible (DT bindings)
> before the patch using that compatible.
> See also: https://elixir.bootlin.com/linux/v6.14-rc6/source/Documentation/devicetree/bindings/submitting-patches.rst#L46
>
> Best regards,
> Krzysztof

Thanks Krzysztof for the suggestion, I will take a look over the doc.

Regards,
Nandor

Re: [PATCH 2/2] dt-bindings: watchdog: fsl-imx: document continue in low power mode

[Nandor Han]

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.
>
> 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,
specifically during simulated high-load scenarios, the device becomes unresponsive because it enters
one of these power states.

> 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.

Regards,
Nandor

Re: [PATCH 2/2] dt-bindings: watchdog: fsl-imx: document continue in low power mode

[Nandor Han]

On 1/6/26 13:51, Peng Fan 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.
>
> Hi Nandor,
>
> 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.
> >From the cover letter, I see that system should reset if runs into
> low power mode. So your system are not allowed to run into low power mode.
>
> If my understanding is correct, DT property should not be used.
> You may need to use sysfs or module_parameter for your case.

Thanks Peng.

Yes, you're correct, our system should not run in low power mode.

My implementation is based on the fact that the driver provides already a Device Tree configuration for the WAIT low power mode.
To maintainconsistency, the patch simply extends support to configure the watchdog during STOP and DOZE power modes.

One important consideration is that the watchdog must be fully configured during boot to catch any potential issues early.
Since this is a hardware property of the watchdog, we considered that device tree is a good place for this configuration.

Regards,
Nandor

Re: [PATCH 2/2] dt-bindings: watchdog: fsl-imx: document continue in low power mode

[Krzysztof Kozlowski]

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.
>>
>> 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

Re: [PATCH 2/2] dt-bindings: watchdog: fsl-imx: document continue in low power mode

[Nandor Han]

On 1/7/26 12:48, 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.
>
> 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.
>>>
>>> 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