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

[Alexandre Belloni <alexandre.belloni@bootlin.com>]

On 09/04/2026 15:44:43+0800, David Wang wrote:
> 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@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.

You need a write-access property. For NXP, we settled with
nxp,write-access.



> 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.

The driver needs to always write 24h mode but can support reading both.



-- 
Alexandre Belloni, co-owner and COO, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com