linux-kernel - Re: [PATCH v2 7/8] du-bindings: mips: cpu: Add img,mips compatible

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Date: Thu, 13 Jun 2024 20:40:18 +0100
From: "Jiaxun Yang" <jiaxun.yang@...goat.com>
To: "Rob Herring" <robh@...nel.org>
Cc: "Conor Dooley" <conor@...nel.org>, "Lee Jones" <lee@...nel.org>,
 "Krzysztof Kozlowski" <krzk+dt@...nel.org>,
 "Conor Dooley" <conor+dt@...nel.org>,
 "paulburton@...nel.org" <paulburton@...nel.org>,
 "Thomas Bogendoerfer" <tsbogend@...ha.franken.de>,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
 "linux-mips@...r.kernel.org" <linux-mips@...r.kernel.org>
Subject: Re: [PATCH v2 7/8] du-bindings: mips: cpu: Add img,mips compatible



在2024年6月13日六月 下午7:59，Rob Herring写道：
> On Wed, Jun 12, 2024 at 05:59:24PM +0100, Jiaxun Yang wrote:
>> 
>> 
>> 在2024年6月12日六月 下午5:39，Conor Dooley写道：
>> > On Wed, Jun 12, 2024 at 12:56:26PM +0100, Jiaxun Yang wrote:
>> >> This compatible is used by boston.dts.
>> >> 
>> >> Signed-off-by: Jiaxun Yang <jiaxun.yang@...goat.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.
>> 
>> 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 kernel.

We can potentially patch this in bootloader, but for existing firmware it'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 limited
circumstances, instead of keeping such usage in grey area.

Thanks

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

-- 
- Jiaxun