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

[Chen-Yu Tsai]

On Tue, Oct 27, 2026 at 5:56 PM Krzysztof Kozlowski <krzk at kernel.org> wrote:
>
> On 27/10/2026 10:39, James Hilliard wrote:
> > 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?
>
> I am confused, there are no other instances here.

I think the point is that it is going to be needed in the future when
we add the compatibles for the SoCs that do have UARTs with different
FIFO sizes.