Thread (19 messages) 19 messages, 4 authors, 2026-01-14

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

From: Krzysztof Kozlowski <krzk@kernel.org>
Date: 2026-01-12 13:56:29
Also in: imx, linux-devicetree, linux-watchdog, lkml

On 08/01/2026 08:58, Nandor Han wrote:
On 1/7/26 12:48, Krzysztof Kozlowski wrote:
quoted
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On 07/01/2026 10:12, Nandor Han wrote:
quoted
On 12/30/25 14:34, Krzysztof Kozlowski wrote:
quoted
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On Mon, Dec 29, 2025 at 04:50:00PM +0200, Nandor Han wrote:
quoted
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).
quoted
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.
quoted
quoted
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.
I want "logical" point of view, not driver's.
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.
Just because you want to do something in the driver is not yet
justification we want it in DT. Why can't you enable it always? Why this
is system load (!!!) dependent?


Best regards,
Krzysztof
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