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Date: Thu, 13 Jun 2024 20:40:18 +0100
From: "Jiaxun Yang" <jiaxun.yang@flygoat.com>
To: "Rob Herring" <robh@kernel.org>
Cc: "Conor Dooley" <conor@kernel.org>, "Lee Jones" <lee@kernel.org>,
 "Krzysztof Kozlowski" <krzk+dt@kernel.org>,
 "Conor Dooley" <conor+dt@kernel.org>,
 "paulburton@kernel.org" <paulburton@kernel.org>,
 "Thomas Bogendoerfer" <tsbogend@alpha.franken.de>,
 devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
 "linux-mips@vger.kernel.org" <linux-mips@vger.kernel.org>
Subject: Re: [PATCH v2 7/8] du-bindings: mips: cpu: Add img,mips compatible
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=E5=9C=A82024=E5=B9=B46=E6=9C=8813=E6=97=A5=E5=85=AD=E6=9C=88 =E4=B8=8B=E5=
=8D=887:59=EF=BC=8CRob Herring=E5=86=99=E9=81=93=EF=BC=9A
> On Wed, Jun 12, 2024 at 05:59:24PM +0100, Jiaxun Yang wrote:
>>=20
>>=20
>> =E5=9C=A82024=E5=B9=B46=E6=9C=8812=E6=97=A5=E5=85=AD=E6=9C=88 =E4=B8=8B=
=E5=8D=885:39=EF=BC=8CConor Dooley=E5=86=99=E9=81=93=EF=BC=9A
>> > On Wed, Jun 12, 2024 at 12:56:26PM +0100, Jiaxun Yang wrote:
>> >> This compatible is used by boston.dts.
>> >>=20
>> >> Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
>> >> ---
>> >> note: This is a wildcard compatible for all MIPS CPUs,
>> >>       I think we should use something like "riscv" for riscv.
>> >
>> > riscv systems, other than simulators etc are not meant to use the
>> > "riscv" compatible. All of the real CPUs use "vendor,cpu", "riscv".
>> > I'd suggest you add specific compatibles for your CPUs.
>>=20
>> Boston can be combined with many different CPUs, thus we need to have
>> such compatibles.
>
> Then you'll need different DTs. Different h/w, different DT.

The board have 9 CPU types in total, with hundreds of different possible
CPU topologies. Maintaining separate DT for them seems impossible in ker=
nel.

We can potentially patch this in bootloader, but for existing firmware i=
t's
being doing like this for years. I can see for RISC-V QEMU generated DTB=
 is
using a single "riscv" compatible and I do think it's a similar problem.

I think it's better to document it and warn people only to use it in lim=
ited
circumstances, instead of keeping such usage in grey area.

Thanks

>
> No way we're taking a generic compatible like this.
>
> Rob

--=20
- Jiaxun