linux-kernel - Re: [PATCH 1/1] dt-bindings: reg-io-width for SiFive CLINT

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Message-ID: <CAEUhbmWFAJpVxproxX-iH3Tj7jHGqu_SwN6-tGuxqi7NXVhOhA@mail.gmail.com>
Date:   Fri, 15 Oct 2021 21:46:01 +0800
From:   Bin Meng <bmeng.cn@...il.com>
To:     Jessica Clarke <jrtc27@...c27.com>
Cc:     Heinrich Schuchardt <heinrich.schuchardt@...onical.com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Guo Ren <guoren@...ux.alibaba.com>, Xiang W <wxjstz@....com>,
        Samuel Holland <samuel@...lland.org>,
        Atish Patra <atish.patra@....com>,
        Rob Herring <robh+dt@...nel.org>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Anup Patel <anup.patel@....com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        devicetree <devicetree@...r.kernel.org>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        OpenSBI <opensbi@...ts.infradead.org>
Subject: Re: [PATCH 1/1] dt-bindings: reg-io-width for SiFive CLINT

On Fri, Oct 15, 2021 at 8:15 PM Jessica Clarke <jrtc27@...c27.com> wrote:
>
> On 15 Oct 2021, at 12:54, Heinrich Schuchardt <heinrich.schuchardt@...onical.com> wrote:
> >
> > On 10/15/21 12:14, Bin Meng wrote:
> >> On Fri, Oct 15, 2021 at 6:09 PM Heinrich Schuchardt
> >> <heinrich.schuchardt@...onical.com> wrote:
> >>>
> >>> The CLINT in the T-HEAD 9xx processors do not support 64bit mmio access to
> >>> the MTIMER device. The current schema does not allow to specify this.
> >>>
> >>> OpenSBI currently uses a property 'clint,has-no-64bit-mmio' to indicate the
> >>> restriction. Samuael Holland suggested in
> >>> lib: utils/timer: Use standard property to specify 32-bit I/O
> >>> https://github.com/smaeul/opensbi/commit/b95e9cf7cf93b0af16fc89204378bc59ff30008e
> >>> to use "reg-io-width = <4>;" as the reg-io-width property is generally used
> >>> in the devicetree schema for such a condition.
> >>>
> >>> A release candidate of the ACLINT specification is available at
> >>> https://github.com/riscv/riscv-aclint/releases
> >>>
> >>> Add reg-io-width as optional property to the SiFive Core Local Interruptor.
> >>>
> >>> Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@...onical.com>
> >>> ---
> >>>  Documentation/devicetree/bindings/timer/sifive,clint.yaml | 7 +++++++
> >>>  1 file changed, 7 insertions(+)
> >>>
> >>> diff --git a/Documentation/devicetree/bindings/timer/sifive,clint.yaml b/Documentation/devicetree/bindings/timer/sifive,clint.yaml
> >>> index a35952f48742..266012d887b5 100644
> >>> --- a/Documentation/devicetree/bindings/timer/sifive,clint.yaml
> >>> +++ b/Documentation/devicetree/bindings/timer/sifive,clint.yaml
> >>> @@ -41,6 +41,13 @@ properties:
> >>>    reg:
> >>>      maxItems: 1
> >>>
> >>> +  reg-io-width:
> >>> +    description: |
> >>> +      Some CLINT implementations, e.g. on the T-HEAD 9xx, only support
> >>> +      32bit access for MTIMER.
> >>> +    $ref: /schemas/types.yaml#/definitions/uint32
> >>> +    const: 4
> >> But this is not a "sifive,clint" anyway. Should there be a new
> >> dt-bindings for T-Head clint variant?
> >
> > I assume by new dt-bindings variant you mean: Add a new compatible string in Documentation/devicetree/bindings/timer/sifive,clint.yaml.
> >
> > The vendor Debian image uses:
> > compatible = "{allwinner,sun20i-d1-clint", "sifive,clint0”};
>
> I assume Bin means to stop calling it a sifive,clint0 and instead have
> something like
>
>     "allwinner,sun20i-d1-clint", "thead,clint0"

Yep, that's what I wanted to see. Sorry for not being clear. The
T-Head CLINT is definitely not compatible with "sifive,clint0".

> as is being done for their non-conforming PLIC. It’s worth pointing out
> that the same is true here; the SiFive CLINT supports 64-bit accesses
> on RV64, so this is not compatible with a SiFive CLINT. Moreover, the
> RISC-V spec was clearly written in a way that intended 64-bit accesses
> to be supported for RV64, though was not completely explicit about
> that, which has now been resolved (see
> https://github.com/riscv/riscv-isa-manual/issues/639), so this CLINT
> violates the obvious intent of the pre-1.12 privileged specs (see
> Andrew’s message in the issue, which agrees with my reading).

Regards,
Bin