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Date:   Mon, 05 Dec 2022 16:54:48 +0000
From:   Conor Dooley <conor@kernel.org>
To:     Icenowy Zheng <uwu@icenowy.me>,
        Conor Dooley <conor.dooley@microchip.com>
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        Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>,
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        Palmer Dabbelt <palmer@dabbelt.com>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Daniel Lezcano <daniel.lezcano@linaro.org>,
        Jisheng Zhang <jszhang@kernel.org>,
        Samuel Holland <samuel@sholland.org>,
        linux-kernel@vger.kernel.org, devicetree@vger.kernel.org,
        linux-riscv@lists.infradead.org
Subject: =?US-ASCII?Q?Re=3A_=5BPATCH_2/3=5D_dt-bindings=3A_timer=3A_si?= =?US-ASCII?Q?five=2Cclint=3A_add_compatible_for_OpenC906?=
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On 5 December 2022 15:59:44 GMT, Icenowy Zheng <uwu@icenowy=2Eme> wrote:
>=E5=9C=A8 2022-12-05=E6=98=9F=E6=9C=9F=E4=B8=80=E7=9A=84 15:05 +0000=EF=
=BC=8CConor Dooley=E5=86=99=E9=81=93=EF=BC=9A
>> On Mon, Dec 05, 2022 at 07:03:17PM +0800, Icenowy Zheng wrote:
>> > =E5=9C=A8 2022-12-05=E6=98=9F=E6=9C=9F=E4=B8=80=E7=9A=84 10:36 +0000=
=EF=BC=8CConor Dooley=E5=86=99=E9=81=93=EF=BC=9A
>>=20
>> > > You lot all know the situation here a lot more than I do=2E=2E=2E
>> > > 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=2E
>> >=20
>> > 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=2E
>> >=20
>> > So I think it okay to just use "thead,c900-clint" here, and when
>> > necessary, try to retrieve mcpuid for dealing with quirks=2E
>>=20
>> I'm not super sure I follow=2E What's the relevance of "mapbaddr" here?
>> We've got a reg property, so I don't think we need "mapbaddr"?
>
>Yes, it's not relevant to us here, it's only to prove that PLIC/CLINT
>is part of C906 "Core Complex"=2E
>
>>=20
>> 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=2E Have I missed something?
>
>These values are set by T-Head instead of individual SoC implementers
>as a CPU CSR, and it's not for uniqueness, but it's for identification
>of the CPU core revision (thus the PLIC/CLINT that come with it)=2E

I really am missing something here that must be obvious to you=2E
Let me try and explain where my gap in understanding is=2E
If someone takes the open cores & makes a minor tweak in the plic how does=
 knowing mcpuid help us identify that that plic is marginally different?

I must have missed something that should be apparent and look like an eeji=
t right now!

>
>>=20
>> > > 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=2E
>> > >=20
>> > > That leaves us with either:
>> > > "vendor,soc-clint", "thead,openc906-clint", "thead,c900-clint"
>> > > or:
>> > > "vendor,soc-clint", "thead,c900-clint"
>> > > right?
>> > >=20
>> > > 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?
>>=20
>