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:   Tue, 2 Aug 2022 22:10:53 +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 2022/08/02 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.

Thank you,

---
Best Regards
Kunihiko Hayashi