Re: [PATCH v4 2/7] dt-bindings: serial: 8250: aspeed: add aspeed,vuart-over-pci bool prop

[Krzysztof Kozlowski <krzk@kernel.org>]

On Wed, Jul 08, 2026 at 03:35:54PM +0000, Grégoire Layet wrote:
> The ASPEED AST2600 has 2 Virtual UARTs accessible over PCI.
> The ASPEED AST2600 can be used as a PCI device.
> 2 Virtual UART can be exposed to the host via this PCI device.
> These are 8250-compatible register sets and can be used to have UART
> communication between the PCI BMC and the host.
> 
> This boolean can be set to specify if a VUART is used over PCI. A VUART
> over PCI needs a syscon phandle. The syscon gives a regmap to the SCU,
> which is used to set the enable bits of the PCI device.
> On the aspeed's chips, the clocks phandle already points at the SCU node.
> But deriving the regmap from the clock provider would misuse the clocks
> binding. An explicit syscon phandle states the dependency directly.
> 
> Signed-off-by: Grégoire Layet <gregoire.layet@9elements.com>
> ---
>  .../devicetree/bindings/serial/8250.yaml      | 22 +++++++++++++++++++
>  1 file changed, 22 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/serial/8250.yaml b/Documentation/devicetree/bindings/serial/8250.yaml
> index 8f22121381fc..2ea8981bba80 100644
> --- a/Documentation/devicetree/bindings/serial/8250.yaml
> +++ b/Documentation/devicetree/bindings/serial/8250.yaml
> @@ -27,6 +27,16 @@ allOf:
>              enum:
>                - aspeed,ast2500-vuart
>                - aspeed,ast2600-vuart
> +  - if:
> +      required:
> +        - aspeed,vuart-over-pci
> +    then:
> +      required:
> +        - syscon
> +      properties:
> +        compatible:
> +          contains:
> +            const: aspeed,ast2600-vuart

else:
...
disallow new properties (see example-schema)

>    - if:
>        properties:
>          compatible:
> @@ -223,6 +233,12 @@ properties:
>            - const: uartclk
>            - const: reg
>  
> +  syscon:

That's explicitly forbidden by writing bindings (and mentioned as the
antipattern in my older talks about DT).

> +    $ref: /schemas/types.yaml#/definitions/phandle
> +    description:
> +      Phandle to the SCU syscon, used to enable the VUART over the BMC PCI
> +      device. Only applicable to aspeed,ast2600-vuart.
> +
>    dmas:
>      minItems: 1
>      maxItems: 4
> @@ -316,6 +332,12 @@ properties:
>        polarity (IRQ_TYPE_LEVEL_LOW or IRQ_TYPE_LEVEL_HIGH). Only
>        applicable to aspeed,ast2500-vuart and aspeed,ast2600-vuart.
>  
> +  aspeed,vuart-over-pci:
> +    type: boolean
> +    description:
> +      Enable the VUART over the BMC PCI device. Only applicable to
> +      aspeed,ast2600-vuart.
> +
>  required:
>    - reg
>    - interrupts
> -- 
> 2.54.0
>