linux-kernel - Re: [PATCH 1/2] dt-bindings: arm64: dts: mediatek: Add mt8395-evk board

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Date:   Tue, 5 Sep 2023 12:58:37 +0200
From:   AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        Macpaul Lin <macpaul.lin@...iatek.com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Frank Wunderlich <frank-w@...lic-files.de>,
        Bernhard Rosenkränzer <bero@...libre.com>,
        Sean Wang <sean.wang@...iatek.com>, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org
Cc:     Bear Wang <bear.wang@...iatek.com>,
        Pablo Sun <pablo.sun@...iatek.com>,
        Macpaul Lin <macpaul@...il.com>,
        Chunfeng Yun <chunfeng.yun@...iatek.com>
Subject: Re: [PATCH 1/2] dt-bindings: arm64: dts: mediatek: Add mt8395-evk
 board

Il 05/09/23 12:36, Krzysztof Kozlowski ha scritto:
> On 05/09/2023 11:36, Macpaul Lin wrote:
>>
>>
>> On 9/4/23 20:11, Krzysztof Kozlowski wrote:
>>> 	
>>>
>>> External email : Please do not click links or open attachments until you
>>> have verified the sender or the content.
>>>
>>> On 04/09/2023 11:50, Macpaul Lin wrote:
>>>>
>>>>
>>>> On 9/4/23 17:33, Krzysztof Kozlowski wrote:
>>>>>
>>>>>
>>>>> External email : Please do not click links or open attachments until you
>>>>> have verified the sender or the content.
>>>>>
>>>>> On 04/09/2023 11:20, Macpaul Lin wrote:
>>>>>> Add bindings for the MediaTek mt8395-evk board.
>>>>>> The mt8359-evk board is also named as "Genio 1200-EVK".
>>>>>> MT8195 and MT8395 are the same family series SoC could share
>>>>>
>>>>> How can be the same and have different numbers? You sill need dedicated
>>>>> compatible.
>>>>>
>>>>
>>>> The SoCs mt8195 and mt8395 are designed for different market application
>>>> and physical characteristics, using different efuse values for
>>>> distinction. The booting flow and configurations are controllered by the
>>>> boot loaders, firmware, and TF-A. Therefore, the part numbers and
>>>> procurement channels are different. The detail information of these
>>>> efuse values is proprietary, so I cant disclose it futher. Hence the
>>>> most of peripheral drivers and base address are almost the same.
>>>
>>> 1. Drivers? So we talk about compatibility, not the same.
>>> 2. "almost the same" is not the same. Follow the guidelines for writing
>>> bindings.
>>>
>>
>> Thanks for the review.
>>
>> After internal confirmation and discussion, it can be confirmed that the
>> MT8195 and MT8395 are identical SoCs from to binding's perspective.
> 
> I am sorry, but I really do not care what you internally discussed about
> bindings. I do not think your internal review respect existing
> guidelines. You talked about drivers, not "bindings perspective", so
> your internal discussion is clearly discussing something else.
> 
>> MediaTek hope the mt8395 boards could directly use mt8195.dtsi, without
>> the need to create a separate mt8395.dtsi to include mt8195.dtsi.
>> Therefore, we hope to fully adopt the bindings of mt8195. However, I
>> will submit a revised patch for compatible since they are different boards.
> 
> You can disagree but then I expect arguments from your side.
> 

In short - they're the same chip, as in, they behave the same on a *hardware*
perspective; what changes is the bootchain (plus stricter security from TF-A)
and allowable temperature ranges for operation, that's practically it...

...so yes the compatible for the "new soc" must be documented, but that's
practically just a revision, *not a new soc* at all.

(though, I agree that seeing a different name as in 1 -> 3 can be totally
confusing)

The drivers difference that Macpaul hinted to are about drivers needing some
SMC calls instead of direct MMIO manipulation, so, something like two bindings
for something like two drivers will need to add a 8395 compatible; speaking of
what we would have in a devicetree for this SoC, that'd be exactly 99% identical
to mt8195.dtsi.

Anyway, drivers are drivers, bindings describe hardware - and the hw is, again,
the same...

Hope that this makes things clearer! :-)

Cheers,
Angelo