[PATCH v3 2/4] dt-bindings: serial: snps-dw-apb-uart: add Allwinner H616

[James Hilliard]

On Tue, Oct 27, 2026 at 2:02 AM Krzysztof Kozlowski <krzk at kernel.org> wrote:
>
> On Sat, Oct 24, 2026 at 02:22:24PM -0600, James Hilliard wrote:
> > The H616 UART has 256-byte transmit and receive FIFOs, but its DesignWare
> > component parameter register does not report the FIFO depth. Its optional
> > register layout also differs from the generic DesignWare integration.
> >
> > Add a specific compatible for the integration and allow the standard
> > fifo-size property to describe the capacity. Require the documented
> > 256-byte size for H616, retaining snps,dw-apb-uart as a fallback.
> >
> > Signed-off-by: James Hilliard <james.hilliard1 at gmail.com>
> > ---
> >  .../devicetree/bindings/serial/snps-dw-apb-uart.yaml    | 17 +++++++++++++++++
> >  1 file changed, 17 insertions(+)
> >
> > diff --git a/Documentation/devicetree/bindings/serial/snps-dw-apb-uart.yaml b/Documentation/devicetree/bindings/serial/snps-dw-apb-uart.yaml
> > index e2ca126d58ba..0f8fd0485879 100644
> > --- a/Documentation/devicetree/bindings/serial/snps-dw-apb-uart.yaml
> > +++ b/Documentation/devicetree/bindings/serial/snps-dw-apb-uart.yaml
> > @@ -13,6 +13,18 @@ allOf:
> >    - $ref: serial.yaml#
> >    - $ref: rs485.yaml#
> >
> > +  - if:
> > +      properties:
> > +        compatible:
> > +          contains:
> > +            const: allwinner,sun50i-h616-uart
> > +    then:
> > +      properties:
> > +        fifo-size:
> > +          const: 256
> > +      required:
> > +        - fifo-size
>
> Why do you require fifo-size if is const? It is implied by the
> compatible.

H616 has a fixed depth, but other sunxi integrations have different
depths between UART instances. For example, D1 has 64-byte FIFOs on
UART0 and 256-byte FIFOs on UART1–5.

Should I keep this explicit for consistency for all sunxi uarts?

>
> > +
> >    - if:
> >        properties:
> >          compatible:
> > @@ -60,6 +72,7 @@ properties:
> >            - const: renesas,rzn1-uart
> >        - items:
> >            - enum:
> > +              - allwinner,sun50i-h616-uart
> >                - anlogic,dr1v90-uart
> >                - brcm,bcm11351-dw-apb-uart
> >                - brcm,bcm21664-dw-apb-uart
> > @@ -120,6 +133,10 @@ properties:
> >        - const: tx
> >        - const: rx
> >
> > +  fifo-size:
> > +    $ref: /schemas/types.yaml#/definitions/uint32
> > +    description: Transmit and receive FIFO capacity in bytes.
>
> Drop property, not used by any of the devices here.
>
> Best regards,
> Krzysztof
>