linux-kernel - Re: [PATCH 07/18] MIPS: DTS: jz4780: fix otg node as reported by dtbscheck

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Message-Id: <81BA49E3-AFDE-4DFD-BB77-2B03488C727B@goldelico.com>
Date:   Sat, 9 Apr 2022 15:53:31 +0200
From:   "H. Nikolaus Schaller" <hns@...delico.com>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        "周琰杰 (Zhou Yanjie)" 
        <zhouyanjie@...yeetech.com>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Paul Cercueil <paul@...pouillou.net>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        linux-mips@...r.kernel.org, letux-kernel@...nphoenux.org
Subject: Re: [PATCH 07/18] MIPS: DTS: jz4780: fix otg node as reported by
 dtbscheck



> Am 09.04.2022 um 15:44 schrieb Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>:
> 
> On 09/04/2022 15:32, H. Nikolaus Schaller wrote:
>> 
>> 
>>> Am 09.04.2022 um 15:15 schrieb Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>:
>>> 
>>> On 09/04/2022 15:05, H. Nikolaus Schaller wrote:
>>>>> 
>>>>> This looks wrong, the block usually should have a specific compatible.
>>>>> Please mention why it does not.
>>>> 
>>>> Well, I did not even have that idea that it could need an explanation.
>>>> 
>>>> There is no "ingenic,jz4780-otg" and none is needed here to make it work.
>>> 
>>> Make it work in what terms? We talk about hardware description, right?
>> 
>> Yes.
>> 
>>> 
>>>> 
>>>> Therefore the generic "snps,dwc2" is sufficient.
>>> 
>>> No, you are mixing now driver behavior (is sufficient) with hardware
>>> description.
>> 
>> No. "snps,dwc2" is a hardware description for a licensed block.
>> Not a driver behavior.
> 
> snps,dwc2 matches the original block, not necessarily this
> implementation. Unless you are sure?

I assume. Nobody has reported an issue without having any specific jz4780 driver in place.
Well, that is only evidence, not bullet proof.

> 
>> 
>>> Most of licensed blocks require the specific compatible to
>>> differentiate it.
>> 
>> If there is a need to differentiate.
> 
> No, regardless whether there is a need currently, most of them have
> specific compatibles, because there are some minor differences. Even if
> difference is not visible from programming model or wiring, it might
> justify it's own specific compatible. For example because maybe once
> that tiny difference will require some changes.
> 
> Someone added the ingenic compatible, so why do you assume that one tool
> (bindings) is correct but other piece of code (using specific
> compatible) is not? You use the argument "bindings warning" which is not
> enough. Argument that blocks are 100% same, is good enough, if you are
> sure. Just use it in commit msg. But are you sure that these are the
> same? Same pins, same programming model (entire model, not used by Linux)?

The compatible ingenic,jz4780-otg was introduced in 158c774d3c64859e84dd20e04d5fb18c8d3d318e.
Hence I have added Yanjie for clarification why he added it in the .dts and not in the bindings.

BR and thanks,
Nikolaus