linux-kernel - Re: [PATCH v2] riscv: sophgo: dts: Add spi controller for SG2042

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Message-ID: <20250303-recital-crunchy-6f7806987da0@wendy>
Date: Mon, 3 Mar 2025 09:08:16 +0000
From: Conor Dooley <conor.dooley@...rochip.com>
To: Chen Wang <unicorn_wang@...look.com>
CC: Conor Dooley <conor@...nel.org>, Zixian Zeng <sycamoremoon376@...il.com>,
	Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>, Paul Walmsley <paul.walmsley@...ive.com>,
	Palmer Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>,
	Inochi Amaoto <inochiama@...look.com>, Alexandre Ghiti <alex@...ti.fr>,
	<devicetree@...r.kernel.org>, <linux-riscv@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>, <sophgo@...ts.linux.dev>,
	<chao.wei@...hgo.com>, <xiaoguang.xing@...hgo.com>
Subject: Re: [PATCH v2] riscv: sophgo: dts: Add spi controller for SG2042

On Sat, Mar 01, 2025 at 09:58:24AM +0800, Chen Wang wrote:
> 
> On 2025/3/1 2:22, Conor Dooley wrote:
> [......]
> > > +
> > > +		spi0: spi@...0004000 {
> > > +			compatible = "snps,dw-apb-ssi";
> > I thought were were dropping the use of "snps,dw-abp-ssi" in isolation,
> > and starting to require soc-specific compatibles now.
> > 
> > Rob, Krzysztof?
> I'm also very interested to know why we can't just use "snps,dw-abp-ssi",
> maybe I missed some discussion ...

Ordinarily you're not allowed to use generic compatibles at all, the
dw stuff has kinda been an ?unofficial? exception for a while and not
just for spi. I think that "exception" has been withdrawn though, and
dw stuff is being brought in line with everything else, but cannot
remember where that started.

> I googled examples of soc-specific defined in the code, and it doesn't seem
> to be much, only arch/mips/boot/dts/mscc/ocelot.dtsi and
> arch/riscv/boot/dts/thead/th1520.dtsi.

> Specially, I looked at the commits for th1520 and saw this https://lore.kernel.org/linux-riscv/20240703-garbage-explicit-bd95f8deb716@wendy/.
> It tells if the fallback works identically, then the specific compatible is
> not needed.

This link is talking about the driver, not the dts/binding. Adding the
device-specific compatible to the driver is only needed if the specific
one has some extra features above and beyond the compatible used as the
fallback.

Cheers,
Conor.

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