linux-kernel - Re: [PATCH v2 2/4] dt-bindings: dma: sf-pdma: add new compatible name

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Message-ID: <20231004133021.GB2743005-robh@kernel.org>
Date:   Wed, 4 Oct 2023 08:30:21 -0500
From:   Rob Herring <robh@...nel.org>
To:     shravan chippa <shravan.chippa@...rochip.com>
Cc:     green.wan@...ive.com, vkoul@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, palmer@...belt.com,
        paul.walmsley@...ive.com, conor+dt@...nel.org,
        dmaengine@...r.kernel.org, devicetree@...r.kernel.org,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        nagasuresh.relli@...rochip.com, praveen.kumar@...rochip.com,
        Conor Dooley <conor.dooley@...rochip.com>
Subject: Re: [PATCH v2 2/4] dt-bindings: dma: sf-pdma: add new compatible name

On Tue, Oct 03, 2023 at 09:52:13AM +0530, shravan chippa wrote:
> From: Shravan Chippa <shravan.chippa@...rochip.com>
> 
> Add new compatible name microchip,mpfs-pdma to support
> out of order dma transfers
> 
> Reviewed-by: Conor Dooley <conor.dooley@...rochip.com>
> Signed-off-by: Shravan Chippa <shravan.chippa@...rochip.com>
> ---
>  .../bindings/dma/sifive,fu540-c000-pdma.yaml         | 12 ++++++++----
>  1 file changed, 8 insertions(+), 4 deletions(-)
> 
> diff --git a/Documentation/devicetree/bindings/dma/sifive,fu540-c000-pdma.yaml b/Documentation/devicetree/bindings/dma/sifive,fu540-c000-pdma.yaml
> index a1af0b906365..974467c4bacb 100644
> --- a/Documentation/devicetree/bindings/dma/sifive,fu540-c000-pdma.yaml
> +++ b/Documentation/devicetree/bindings/dma/sifive,fu540-c000-pdma.yaml
> @@ -27,10 +27,14 @@ allOf:
>  
>  properties:
>    compatible:
> -    items:
> -      - enum:
> -          - sifive,fu540-c000-pdma
> -      - const: sifive,pdma0
> +    oneOf:
> +      - items:
> +          - const: microchip,mpfs-pdma # Microchip out of order DMA transfer
> +          - const: sifive,fu540-c000-pdma # Sifive in-order DMA transfer

This doesn't really make sense. microchip,mpfs-pdma is compatible with 
sifive,fu540-c000-pdma and sifive,fu540-c000-pdma is compatible with 
sifive,pdma0, but microchip,mpfs-pdma is not compatible with 
sifive,pdma0? (Or replace "compatible with" with "a superset of")

Any fallback is only useful if an OS only understanding the fallback 
will work with the h/w. Does this h/w work without the driver changes?

Rob