linux-kernel - Re: [PATCH v2] dt-bindings: dma: xilinx: Add power-domains to xlnx,zynqmp-dpdma

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Date:   Wed, 3 May 2023 16:09:34 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Michal Simek <michal.simek@....com>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:     linux-kernel@...r.kernel.org, monstr@...str.eu,
        michal.simek@...inx.com, git@...inx.com,
        Hyun Kwon <hyun.kwon@...inx.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Vinod Koul <vkoul@...nel.org>, devicetree@...r.kernel.org,
        dmaengine@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2] dt-bindings: dma: xilinx: Add power-domains to
 xlnx,zynqmp-dpdma

On 03/05/2023 15:27, Michal Simek wrote:
> Hi,
> 
> On 5/3/23 14:51, Laurent Pinchart wrote:
>> Hi Michal,
>>
>> Thank you for the patch.
>>
>> On Wed, May 03, 2023 at 10:00:20AM +0200, Michal Simek wrote:
>>> DP DMA has own power domain that's why describe optional power-domain
>>> property.
>>
>> As far as I understand, the property should always be specified, the
>> only reason why it's not mandatory is backward-compatibility (I would
>> make it mandatory, as I think proper validation of new DT is more
>> important than avoiding breaking validation - but not operation! - of
>> old DT, but that's a separate story). If my understanding is correct,
>> could you please update the example in the bindings to add the
>> power-domains property ?
> 
> backward compatible - of course
> always specified - if pd driver is enabled it must be there. If not it doesn't 
> do anything - just describes it.
> 
> I am not in a position to decide this. But if dt folks agree with your ask I am 
> happy to make it mandatory and extend example.

By making it mandatory in the bindings only, not in the driver, no real
ABI gets broken. Linux won't stop booting if property is missing.
Therefore if device is always part of power domain and it is actually
required, then sure - making it required is useful.

Best regards,
Krzysztof