linux-kernel - Re: [PATCH 9/9] ARM: dts: uniphier: Remove compatible "snps,dw-pcie-ep" from Pro5 pcie-ep node

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Message-ID: <445840cd-84e3-40bc-223f-4feacbcbcdf6@socionext.com>
Date:   Thu, 4 Aug 2022 15:26:31 +0900
From:   Kunihiko Hayashi <hayashi.kunihiko@...ionext.com>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        Arnd Bergmann <arnd@...db.de>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 9/9] ARM: dts: uniphier: Remove compatible
 "snps,dw-pcie-ep" from Pro5 pcie-ep node

On 2022/08/03 15:11, Krzysztof Kozlowski wrote:
> On 02/08/2022 15:10, Kunihiko Hayashi wrote:
>> On 2022/08/02 17:33, Krzysztof Kozlowski wrote:
>>> On 30/07/2022 13:58, Arnd Bergmann wrote:
>>>> On Mon, Jul 4, 2022 at 2:20 AM Kunihiko Hayashi
>>>> <hayashi.kunihiko@...ionext.com> wrote:
>>>>>
>>>>> UniPhier PCIe endpoint controller doesn't use "snps,dw-pcie-ep"
>>>>> compatible,
>>>>> so this is no longer needed. Remove the compatible string from the
>>>>> pcie-ep
>>>>> node to fix the following warning.
>>>>>
>>>>>     uniphier-pro5-epcore.dtb: pcie@...00000: compatible:
>>>>> ['socionext,uniphier-pro5-pcie-ep', 'snps,dw-pcie-ep'] is too long
>>>>>         From schema:
>>>>> Documentation/devicetree/bindings/pci/socionext,uniphier-pcie-ep.yaml
>>>>>
>>>>
>>>> This sounds like a problem with the binding rather than the dt file. Is
>>>> this not
>>>> a designware pci endpoint? Should it be documented in that binding
>>>> instead?
>>
>> In term of the binding, it seems that the current binding doesn't allow
>> descriptions
>> that list two compatibles. There is something wrong with the binding.
>>
>>> Depends. We had one or two similar cases, where we dropped the snps/dw
>>> generic compatible, because device was actually quite different and
>>> could not match against snps/dw compatible. IOW, if device bound/matched
>>> via generic compatible it would be entirely non-operational. Logically I
>>> think it is okay to drop the generic compatible. Different question is
>>> any ABI break.
>>
>> In term of the controller, we can add dw general compatible if the more
>> generic
>> driver (pcie-designware-plat) works on the controller.
>>
>> However, the generic driver can't do the initialization what the
>> controller
>> needs, so we can add controller-specific compatible only.
>> The commit bf2942a8b7c3 ("arm64: tegra: Fix Tegra194 PCIe EP compatible
>> string")
>> removes the generic compatible for the same reason.
>>
>> This patch suggests removing the generic compatible for the former reason,
>> though, I might suggest it for the controller reason.
> 
> The patch does not explain this, though.

Yes, I'll resend the patch with an explanation of the reason for the controller
like Tegra194.

Thank you,

---
Best Regards
Kunihiko Hayashi