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

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Date:   Wed, 3 Aug 2022 08:11:56 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Kunihiko Hayashi <hayashi.kunihiko@...ionext.com>,
        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 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.


Best regards,
Krzysztof