linux-kernel - Re: [PATCH v4 2/3] dt-bindings: Add dma-channels for pdma device node

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Date:   Thu, 20 Jan 2022 10:51:55 -0800 (PST)
From:   Palmer Dabbelt <palmer@...belt.com>
To:     zong.li@...ive.com
CC:     robh+dt@...nel.org, Paul Walmsley <paul.walmsley@...ive.com>,
        aou@...s.berkeley.edu, krzysztof.kozlowski@...onical.com,
        conor.dooley@...rochip.com, geert@...ux-m68k.org,
        bin.meng@...driver.com, green.wan@...ive.com, vkoul@...nel.org,
        dmaengine@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org,
        zong.li@...ive.com
Subject:     Re: [PATCH v4 2/3] dt-bindings: Add dma-channels for pdma device node

On Sun, 16 Jan 2022 17:35:27 PST (-0800), zong.li@...ive.com wrote:
> Add dma-channels property, then we can determine how many channels there
> by device tree, rather than statically defines it in PDMA driver

Maybe "statically defining it" is better here?

>
> Signed-off-by: Zong Li <zong.li@...ive.com>
> ---
>  .../devicetree/bindings/dma/sifive,fu540-c000-pdma.yaml    | 7 +++++++
>  1 file changed, 7 insertions(+)
>
> diff --git a/Documentation/devicetree/bindings/dma/sifive,fu540-c000-pdma.yaml b/Documentation/devicetree/bindings/dma/sifive,fu540-c000-pdma.yaml
> index d32a71b975fe..3dbb8caefc17 100644
> --- a/Documentation/devicetree/bindings/dma/sifive,fu540-c000-pdma.yaml
> +++ b/Documentation/devicetree/bindings/dma/sifive,fu540-c000-pdma.yaml
> @@ -34,6 +34,12 @@ properties:
>      minItems: 1
>      maxItems: 8
>
> +  dma-channels:
> +    description: For backwards-compatible, the default value is 4

Maybe "backwards-compatibility" is better here?

> +    minimum: 1
> +    maximum: 4
> +    default: 4
> +
>    '#dma-cells':
>      const: 1
>
> @@ -50,6 +56,7 @@ examples:
>      dma@...0000 {
>        compatible = "sifive,fu540-c000-pdma";

IMO we should have a "sifive,pdma-1.0.0" (or whatever the versioning 
scheme ended up being) here, in addition to the SOC-specific DT entry.  
It's kind of odd to start extending the SOC-specific DT entry, as the 
whole idea there is to let us have an out in case we find future 
compatibility issues.

>        reg = <0x3000000 0x8000>;
> +      dma-channels = <4>;
>        interrupts = <23 24 25 26 27 28 29 30>;
>        #dma-cells = <1>;
>      };