linux-kernel - Re: [PATCH 2/3] dt-bindings: timer: sifive,clint: add compatible for OpenC906

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Message-ID: <Y44IoC765yztZ6VF@wendy>
Date:   Mon, 5 Dec 2022 15:05:04 +0000
From:   Conor Dooley <conor.dooley@...rochip.com>
To:     Icenowy Zheng <uwu@...nowy.me>
CC:     Conor Dooley <conor@...nel.org>, Rob Herring <robh@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        Marc Zyngier <maz@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Jisheng Zhang <jszhang@...nel.org>,
        Samuel Holland <samuel@...lland.org>,
        <linux-kernel@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-riscv@...ts.infradead.org>
Subject: Re: [PATCH 2/3] dt-bindings: timer: sifive,clint: add compatible for
 OpenC906

On Mon, Dec 05, 2022 at 07:03:17PM +0800, Icenowy Zheng wrote:
> 在 2022-12-05星期一的 10:36 +0000，Conor Dooley写道：

> > You lot all know the situation here a lot more than I do...
> > I don't think "letting" people use the bare "thead,c900-foo" makes
> > much
> > sense as it gives us no chance to deal with quirks down the line.
> 
> Well, after rechecking the manual, I found it possible to handle quirks
> -- T-Head has a custom "mcpuid" CSR (@ RISC-V CSR 0xFC0), which can be
> used to retrieve some identification info of the core, including its
> model ID, version, etc; and the T-Head PLIC/CLINT are part of their
> C906 SoC design that there's another "mapbaddr" CSR that could be used
> to retrieve the base address of them.
> 
> So I think it okay to just use "thead,c900-clint" here, and when
> necessary, try to retrieve mcpuid for dealing with quirks.

I'm not super sure I follow. What's the relevance of "mapbaddr" here?
We've got a reg property, so I don't think we need "mapbaddr"?

For "mcpuid", can you be sure that implementers will not omit setting
that value to something unique? I'd be happier if we were overly clear
now rather than have some headaches later. Have I missed something?

> > I don't think that using "thead,openc906-clint", "thead,c900-clint"
> > makes all that much sense either, in case someone does something
> > wacky
> > with the open-source version of the core.
> > 
> > That leaves us with either:
> > "vendor,soc-clint", "thead,openc906-clint", "thead,c900-clint"
> > or:
> > "vendor,soc-clint", "thead,c900-clint"
> > right?
> > 
> > The first one seems like possibly the better option as you'd kinda
> > expect that, in a perfect word, all of the open-source IP
> > implementations would share quirks etc?


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