Re: [PATCH 06/11] dt-bindings: dma: stm32-dma3: introduce st,axi-max-burst-len property

[Rob Herring <robh@kernel.org>]

On Thu, Oct 10, 2024 at 04:27:56PM +0200, Amelie Delaunay wrote:
> DMA3 maximum burst length (in unit of beat) may be restricted depending
> on bus interconnect.
> 
> As mentionned in STM32MP2 reference manual [1], "the maximum allowed AXI
> burst length is 16. The user must set [S|D]BL_1 lower or equal to 15
> if the Source/Destination allocated port is AXI (if [S|D]AP=0)".

This should be implied by the SoC specific compatible.

> 
> Introduce st,axi-max-burst-len. If used, it will clamp the burst length
> to that value if AXI port is used, if not, the maximum burst length value
> supported by DMA3 is used.
> 
> [1] https://www.st.com/resource/en/reference_manual/rm0457-stm32mp2325xx-advanced-armbased-3264bit-mpus-stmicroelectronics.pdf
> 
> Signed-off-by: Amelie Delaunay <amelie.delaunay@foss.st.com>
> ---
>  .../devicetree/bindings/dma/stm32/st,stm32-dma3.yaml          | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/dma/stm32/st,stm32-dma3.yaml b/Documentation/devicetree/bindings/dma/stm32/st,stm32-dma3.yaml
> index 38c30271f732e0c8da48199a224a88bb647eeca7..90ad70bb24eb790afe72bf2085478fa4cec60b94 100644
> --- a/Documentation/devicetree/bindings/dma/stm32/st,stm32-dma3.yaml
> +++ b/Documentation/devicetree/bindings/dma/stm32/st,stm32-dma3.yaml
> @@ -51,6 +51,16 @@ properties:
>    power-domains:
>      maxItems: 1
>  
> +  st,axi-max-burst-len:
> +    description: |
> +      Restrict AXI burst length in unit of beat by value specified in this property.
> +      The value specified in this property is clamped to the maximum burst length supported by DMA3.
> +      If this property is missing, the maximum burst length supported by DMA3 is used.
> +    $ref: /schemas/types.yaml#/definitions/uint32
> +    minimum: 1
> +    maximum: 256
> +    default: 64
> +
>    "#dma-cells":
>      const: 3
>      description: |
> @@ -137,5 +147,6 @@ examples:
>                     <GIC_SPI 48 IRQ_TYPE_LEVEL_HIGH>;
>        clocks = <&rcc CK_BUS_HPDMA1>;
>        #dma-cells = <3>;
> +      st,axi-max-burst-len = <16>;
>      };
>  ...
> 
> -- 
> 2.25.1
>