linux-kernel - Re: [PATCH v2 1/1] dt-bindings: reg-io-width for SiFive CLINT

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Message-ID: <CAAhSdy3JU6jitTWFk4CVRG5Xc7P7ueZzd=xmnKBNpx8eGaR6hw@mail.gmail.com>
Date:   Mon, 18 Oct 2021 10:03:04 +0530
From:   Anup Patel <anup@...infault.org>
To:     Heinrich Schuchardt <heinrich.schuchardt@...onical.com>
Cc:     Daniel Lezcano <daniel.lezcano@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Guo Ren <guoren@...ux.alibaba.com>,
        Bin Meng <bmeng.cn@...il.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@...r.kernel.org List" <linux-kernel@...r.kernel.org>,
        DTML <devicetree@...r.kernel.org>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        OpenSBI <opensbi@...ts.infradead.org>
Subject: Re: [PATCH v2 1/1] dt-bindings: reg-io-width for SiFive CLINT

On Fri, Oct 15, 2021 at 5:37 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.
> Add a new compatible string "allwinner,sun20i-d1-clint" for the CLINT of
> the Allwinner D1 SoC.
>
> Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@...onical.com>
> ---
>  .../devicetree/bindings/timer/sifive,clint.yaml     | 13 +++++++++++--
>  1 file changed, 11 insertions(+), 2 deletions(-)
>
> diff --git a/Documentation/devicetree/bindings/timer/sifive,clint.yaml b/Documentation/devicetree/bindings/timer/sifive,clint.yaml
> index a35952f48742..d3b4c6844e2f 100644
> --- a/Documentation/devicetree/bindings/timer/sifive,clint.yaml
> +++ b/Documentation/devicetree/bindings/timer/sifive,clint.yaml
> @@ -26,6 +26,7 @@ properties:
>        - enum:
>            - sifive,fu540-c000-clint
>            - canaan,k210-clint
> +          - allwinner,sun20i-d1-clint
>        - const: sifive,clint0
>
>      description:
> @@ -33,14 +34,22 @@ properties:
>        Supported compatible strings are -
>        "sifive,fu540-c000-clint" for the SiFive CLINT v0 as integrated
>        onto the SiFive FU540 chip, "canaan,k210-clint" for the SiFive
> -      CLINT v0 as integrated onto the Canaan Kendryte K210 chip, and
> -      "sifive,clint0" for the SiFive CLINT v0 IP block with no chip
> +      CLINT v0 as integrated onto the Canaan Kendryte K210 chip,
> +      "allwinner,sun20i-d1-clint" for the CLINT in the Allwinner D1 SoC,
> +      and "sifive,clint0" for the SiFive CLINT v0 IP block with no chip
>        integration tweaks.
>        Please refer to sifive-blocks-ip-versioning.txt for details
>
>    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
> +

Please drop the "reg-io-width" DT property.

Based on discussion on ACLINT MTIMER DT bindings, Rob suggested
using implementation specific compatible string for detecting register IO
width. We should follow the same strategy here as well.

Regards,
Anup

>    interrupts-extended:
>      minItems: 1
>
> --
> 2.32.0
>