linux-kernel - Re: [PATCH 13/14] dt-bindings: dma: dma350: Support ARM DMA-250

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Message-ID: <c178a775-5953-4b20-b37d-87a8559c8062@arm.com>
Date: Fri, 29 Aug 2025 12:16:43 +0100
From: Robin Murphy <robin.murphy@....com>
To: Krzysztof Kozlowski <krzk@...nel.org>, Jisheng Zhang
 <jszhang@...nel.org>, Vinod Koul <vkoul@...nel.org>,
 Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
 Conor Dooley <conor+dt@...nel.org>
Cc: dmaengine@...r.kernel.org, devicetree@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 13/14] dt-bindings: dma: dma350: Support ARM DMA-250

On 2025-08-23 5:11 pm, Krzysztof Kozlowski wrote:
> On 23/08/2025 17:40, Jisheng Zhang wrote:
>> Compared with ARM DMA-350, DMA-250 is a simplified version, they share
>> many common parts, but they do have difference. The difference will be
>> handled in next driver patch, while let's add DMA-250 compatible string
>> to dt-binding now.
>>
>> Signed-off-by: Jisheng Zhang <jszhang@...nel.org>
>> ---
>>   Documentation/devicetree/bindings/dma/arm,dma-350.yaml | 1 +
>>   1 file changed, 1 insertion(+)
>>
>> diff --git a/Documentation/devicetree/bindings/dma/arm,dma-350.yaml b/Documentation/devicetree/bindings/dma/arm,dma-350.yaml
>> index 94752516e51a..d49736b7de5e 100644
>> --- a/Documentation/devicetree/bindings/dma/arm,dma-350.yaml
>> +++ b/Documentation/devicetree/bindings/dma/arm,dma-350.yaml
>> @@ -15,6 +15,7 @@ allOf:
>>   properties:
>>     compatible:
>>       const: arm,dma-350
>> +    const: arm,dma-250
> 
> This obviously cannot work and was NEVER tested. Please test your code
> before you send it to mailing lists.

Also, DMA-250 should be 100% "compatible" with DMA-350 in the DT sense, 
since it shares the same register layout and general functionality, and 
the detailed features and even exact model are discoverable from ID 
registers (hence why the current driver explicitly checks for 
PRODUCTID_DMA350 as that's the only one it knows it definitely understands).

Thanks,
Robin.