[PATCH 1/2] dt-bindings: rtc: nct3018y: add nuvoton,ctrl-reg-val property

[David Wang]

On Apr 9, 2026, at 15:23, Krzysztof Kozlowski wrote:
>
> On 09/04/2026 09:21, David Wang wrote:
> > Add "nuvoton,ctrl-reg-val" vendor property to allow optional
> > initialization of the RTC control register (0x0A).
> >
> > This allows platform-specific configurations like 24h mode and
> > write ownership to be defined via Device Tree.
> >
> > Signed-off-by: David Wang <tomato1220 at gmail.com>
> > ---
> >  Documentation/devicetree/bindings/rtc/nuvoton,nct3018y.yaml | 5 +++++
> >  1 file changed, 5 insertions(+)
> >
> > diff --git a/Documentation/devicetree/bindings/rtc/nuvoton,nct3018y.yaml b/Documentation/devicetree/bindings/rtc/nuvoton,nct3018y.yaml
> > index 4f9b5604acd9..0984dfb77170 100644
> > --- a/Documentation/devicetree/bindings/rtc/nuvoton,nct3018y.yaml
> > +++ b/Documentation/devicetree/bindings/rtc/nuvoton,nct3018y.yaml
> > @@ -24,6 +24,10 @@ properties:
> >
> >    reset-source: true
> >
> > +  nuvoton,ctrl-reg-val:
> > +    $ref: /schemas/types.yaml#/definitions/uint32
> > +    description: Initial value for the control register (0x0A).
>
> 24h mode is not a property of a board. I don't know what "write
> ownership" is.
>
> Best regards,
> Krzysztof

Hi Krzysztof,

Thanks for your feedback. Let me clarify these two points based on the
NCT3018Y datasheet:
1. Regarding "write ownership": The NCT3018Y features two I2C
interfaces (Primary and Secondary). The TWO (Time Write Ownership) bit
in the control register determines which interface has the authority
to write to the RTC. We need to ensure the interface connected to our
SoC is granted this ownership during probe—especially for factory-new
chips—to ensure the RTC is writable.
2. Regarding "24h mode": This bit determines the internal data format
in which time is stored within the RTC hardware. Setting this ensures
the hardware's internal storage layout matches the driver's
expectation from the start.

Best regards,
David Wang