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

[James Hilliard]

On Tue, Oct 27, 2026 at 4:05 AM Krzysztof Kozlowski <krzk@xxxxxxxxxx> wrote:
>
> On 27/10/2026 11:02, Chen-Yu Tsai wrote:
> >>>>> +  - 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.
>
> Then we add it. We don't create code which is not used.

On further investigation it appears the sunxi boards with UARTS with
different FIFO sizes might all have a register for reading the FIFO size
at runtime via FCC capacity bits so I guess we might not even need
a fifo-size device tree property for any sunxi boards if that is the case,
not entirely sure if all mixed FIFO size boards support this however but
I have yet to come across one that doesn't.

>
> Best regards,
> Krzysztof