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Date:   Tue, 06 Dec 2022 06:33:13 +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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        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 6 December 2022 03:46:11 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 16:54 +0000=EF=
=BC=8CConor Dooley=E5=86=99=E9=81=93=EF=BC=9A
>>=20
>>=20
>> 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 +0=
000=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"?
>> >=20
>> > Yes, it's not relevant to us here, it's only to prove that
>> > PLIC/CLINT
>> > is part of C906 "Core Complex"=2E
>> >=20
>> > >=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?
>> >=20
>> > 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
>>=20
>> 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?
>
>No, but my point is that in this situation we shouldn't use C900
>compatible at all because it's no longer the vanilla C900 cores=2E
>
>My assumption is that the same IP cores are the same unless specially
>customized=2E

Ah see that is assuming people get it right=2E
I've been in the mindset of "what if the difference is only noticed after =
the DT has been shipped"=2E
I guess that's where we've been at odds=2E

>
>>=20
>> I must have missed something that should be apparent and look like an
>> eejit right now!
>>=20
>> >=20
>> > >=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
>> >=20
>