linux-kernel - Re: [PATCH 1/3] dt-bindings: i2c: mv64xxx: Document DMA properties

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Date:   Tue, 30 Aug 2022 08:10:01 -0500
From:   Samuel Holland <samuel@...lland.org>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        Chen-Yu Tsai <wens@...e.org>,
        Jernej Skrabec <jernej.skrabec@...il.com>
Cc:     Gregory CLEMENT <gregory.clement@...tlin.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Rob Herring <robh+dt@...nel.org>, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-i2c@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-sunxi@...ts.linux.dev
Subject: Re: [PATCH 1/3] dt-bindings: i2c: mv64xxx: Document DMA properties

On 8/30/22 4:36 AM, Krzysztof Kozlowski wrote:
> On 30/08/2022 05:08, Samuel Holland wrote:
>> Allwinner's I2C offload engine includes bidirectional DMA support. Add
>> the properties for describing this in the devicetree. "dmas" is optional
>> because not all instances of the controller have their DRQs hooked up.
>> For example, R_I2C0 and R_I2C1 on V536 have no DRQ number assigned.
>>
>> Signed-off-by: Samuel Holland <samuel@...lland.org>
> 
> Thank you for your patch. There is something to discuss/improve.
> 
>> ---
>>
>>  .../bindings/i2c/marvell,mv64xxx-i2c.yaml           | 13 +++++++++++++
>>  1 file changed, 13 insertions(+)
>>
>> diff --git a/Documentation/devicetree/bindings/i2c/marvell,mv64xxx-i2c.yaml b/Documentation/devicetree/bindings/i2c/marvell,mv64xxx-i2c.yaml
>> index 0ec033e48830..63d665a4f9bb 100644
>> --- a/Documentation/devicetree/bindings/i2c/marvell,mv64xxx-i2c.yaml
>> +++ b/Documentation/devicetree/bindings/i2c/marvell,mv64xxx-i2c.yaml
>> @@ -66,6 +66,19 @@ properties:
>>    resets:
>>      maxItems: 1
>>  
>> +  dmas:
>> +    items:
>> +      - description: RX DMA Channel
>> +      - description: TX DMA Channel
>> +
>> +  dma-names:
>> +    items:
>> +      - const: rx
>> +      - const: tx
>> +
>> +dependencies:
>> +  dmas: [ dma-names ]
> 
> Dependency is not needed. meta-schema has it.

The only dma-names dependencies I see in dtschema (meta-schemas/dma.yaml and
schemas/dma/dma.yaml) are in the other direction. Those are saying that
dma-names only makes sense if dmas is provided.

Here I am saying that the two DMA requests are optional, but only optional
"together". The node must either have no DMA properties or both DMA properties.

Regards,
Samuel