linux-kernel - Re: [PATCH v2 1/3] dt-bindings: dma: snps,dw-axi-dmac: Add reset items

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Date:   Fri, 24 Feb 2023 14:21:21 +0100
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Walker Chen <walker.chen@...rfivetech.com>,
        Eugeniy Paltsev <Eugeniy.Paltsev@...opsys.com>,
        Vinod Koul <vkoul@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor@...nel.org>,
        Palmer Dabbelt <palmer@...belt.com>,
        Emil Renner Berthing <kernel@...il.dk>,
        Emil Renner Berthing <emil.renner.berthing@...onical.com>
Cc:     dmaengine@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org
Subject: Re: [PATCH v2 1/3] dt-bindings: dma: snps,dw-axi-dmac: Add reset
 items

On 24/02/2023 14:09, Walker Chen wrote:
> 
> 
> On 2023/2/24 18:51, Krzysztof Kozlowski wrote:
>> On 24/02/2023 11:14, Walker Chen wrote:
>>>>>    resets:
>>>>> -    maxItems: 1
>>>>> +    maxItems: 2
>>>>
>>>> This breaks ABI and all other users. Test your changes before sending.
>>>
>>> I think 'minItems' should be added here. So like this:
>>> resets:
>>>   minItems: 1
>>>   maxItems: 2
>>>
>>> Other platform/users will not be affected by this.
>>
>> Which will allow two resets on all platforms. Is this correct for these
>> platforms? Do they have two resets?
>>
> In kernel 6.2, only two platforms use this DMA controller (see 'arch/arc/boot/dts/hsdk.dts' and 'arch/riscv/boot/dts/canaan/k210.dtsi').

What about all out-of-tree platforms, bootloaders and FW?

> There is one reset on k210, while there is no reset of DMA on hsdk at all.
> If here minItems with value 1 is added and the value of maxItems is changed to 2, after my testing,
> whether it is one reset or two resets, even no reset, there is no errors occur when doing dtbs_check,

Yeah, I know how this works.

> the DMA initialization shall not be affected either on their platforms.

I asked whether the hardware physically have two resets. dtbs_check
checks the DTS, not the hardware. You know allow two resets for each
other variant. What's more, you call first reset axi for all variants.
This does not look correct, e.g. k210.dtsi does not indicate this is axi
reset line but reset for entire block.

Thus your change should be constrained per your variant (min/max in
top-level, allOf:if:then allowing two lines for you, disallowing for
others).



Best regards,
Krzysztof