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

[Krzysztof Kozlowski]

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.

Best regards,
Krzysztof