Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <879345cd8609cddccbf7bcf230923139af320b17.camel@icenowy.me>
Subject: Re: [PATCH 2/3] dt-bindings: timer: sifive,clint: add compatible
 for OpenC906
From:   Icenowy Zheng <uwu@icenowy.me>
To:     Conor Dooley <conor.dooley@microchip.com>
Cc:     Conor Dooley <conor@kernel.org>, Rob Herring <robh@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>,
        Marc Zyngier <maz@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        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
Date:   Mon, 05 Dec 2022 23:59:44 +0800
In-Reply-To: <Y44IoC765yztZ6VF@wendy>
References: <20221121041757.418645-3-uwu@icenowy.me>
         <98005150-83a7-5439-0db1-d93d459c3809@linaro.org>
         <b924d37d716fa8b1fd93102b1d51fac221f43d59.camel@icenowy.me>
         <d0f3ce4f-5676-f5e1-f04f-dd069679b2d3@linaro.org>
         <81C2234E-C92D-4F78-8295-7C6DD0A9BBC4@icenowy.me>
         <20221130181330.GA2544489-robh@kernel.org> <Y4j+Gpptk3NAFBNV@spud>
         <4ad56fa249a30167844abcedac53d198606511d8.camel@icenowy.me>
         <Y43Jt3YOSbFyh954@wendy>
         <75a3ef9a175b16c46b57b2829ecbe4f97737de8a.camel@icenowy.me>
         <Y44IoC765yztZ6VF@wendy>
Organization: Anthon Open-Source Community
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
User-Agent: Evolution 3.44.4 
MIME-Version: 1.0
Precedence: bulk

=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...
> > > 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.
> >=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.
> >=20
> > So I think it okay to just use "thead,c900-clint" here, and when
> > necessary, try to retrieve mcpuid for dealing with quirks.
>=20
> 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"?

Yes, it's not relevant to us here, it's only to prove that PLIC/CLINT
is part of C906 "Core Complex".

>=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. 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).

>=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.
> > >=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