linux-kernel - Re: [PATCH v2 1/6] riscv: dts: sophgo: Put sdhci compatible in dt of specific SoC

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Message-ID: <6a993b58-3d9e-4f92-bf47-7692c9639314@sifive.com>
Date: Mon, 17 Jun 2024 10:57:54 -0500
From: Samuel Holland <samuel.holland@...ive.com>
To: Jisheng Zhang <jszhang@...nel.org>,
 Thomas Bonnefille <thomas.bonnefille@...tlin.com>
Cc: Yixun Lan <dlan@...too.org>, Inochi Amaoto <inochiama@...look.com>,
 Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
 Conor Dooley <conor+dt@...nel.org>, Paul Walmsley
 <paul.walmsley@...ive.com>, Chen Wang <unicorn_wang@...look.com>,
 Chao Wei <chao.wei@...hgo.com>, Albert Ou <aou@...s.berkeley.edu>,
 Palmer Dabbelt <palmer@...belt.com>, Thomas Gleixner <tglx@...utronix.de>,
 Daniel Lezcano <daniel.lezcano@...aro.org>,
 Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
 Miquèl Raynal <miquel.raynal@...tlin.com>,
 linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
 linux-riscv@...ts.infradead.org, Conor Dooley <conor@...nel.org>
Subject: Re: [PATCH v2 1/6] riscv: dts: sophgo: Put sdhci compatible in dt of
 specific SoC

Hi Jisheng, Thomas,

On 2024-06-17 10:40 AM, Conor Dooley wrote:
> On Mon, Jun 17, 2024 at 09:16:43PM +0800, Jisheng Zhang wrote:
>> On Mon, Jun 17, 2024 at 11:16:32AM +0200, Thomas Bonnefille wrote:
>>> On 6/17/24 1:58 AM, Yixun Lan wrote:
>>>> On 18:47 Wed 12 Jun     , Inochi Amaoto wrote:
> 
>>>>> Is this change necessary? IIRC, the sdhci is the same across
>>>>> the whole series.
> 
>> sorry for being late, I was busy in the past 2.5 month. Per my
>> understanding, the sdhci in cv1800b is the same as the one in
>> sg200x. Maybe I'm wrong, but this was my impression when I cooked
>> the sdhci driver patch for these SoCs.
>>
>>>> I tend to agree with Inochi here, if it's same across all SoC, then no bother to
>>>> split, it will cause more trouble to maintain..
>>>>
>>>
>>> To be honest, I agree with this to, but as a specific compatible for the
>>> SG2002 was created in commit 849e81817b9b, I thought that the best practice
>>> was to use it.
>>
>> I'd like to take this chance to query DT maintainers: FWICT, in the past
>> even if the PLIC is the same between SoCs, adding a new compatible for
>> them seems a must. So when time goes on, the compatbile list would be
>> longer and longer, is it really necessary? Can we just use the existing
>> compatible string?
>> DT maintainers may answered the query in the past, if so, sorry for
>> querying again.
> 
> For new integrations of an IP, yes, new specific compatibles please. New
> integrations may have different bugs etc, even if the IP itself is the
> same. If there's different SoCs that are the same die, but with elements
> fused off, then sure, use the same compatible.
> 
> I expect the list of compatibles in the binding to grow rather large, but
> that is fine. No one SoC is going to do anything other than something like
> compatible = "renesas,$soc-plic", "andestech,corecomplex-plic", "riscv,plic";
> which I think is perfectly fine.

And you can do the same thing here for the SDHCI controller: if you think sg200x
has the same controller (and integration! e.g. number of clocks/resets) as
cv1800b, then you should keep sophgo,cv1800b-dwcmshc as a fallback compatible
string. Then the driver doesn't need any changes until/unless you eventually
find some reason they are not compatible.

It's better to have a SoC-specific compatible string in the DT and not need it,
than find out later you need one and not have it. :)

Regards,
Samuel