linux-kernel - Re: [PATCH v4 1/2] dt-bindings: timer: thead,c900-aclint-mtimer: separate mtime and mtimecmp regs

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Message-ID: <20231120-banshee-traverse-554723cd9490@spud>
Date:   Mon, 20 Nov 2023 16:52:03 +0000
From:   Conor Dooley <conor@...nel.org>
To:     Inochi Amaoto <inochiama@...look.com>
Cc:     Daniel Lezcano <daniel.lezcano@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Chen Wang <unicorn_wang@...look.com>,
        Anup Patel <anup@...infault.org>,
        Samuel Holland <samuel.holland@...ive.com>,
        Guo Ren <guoren@...nel.org>,
        Jisheng Zhang <jszhang@...nel.org>,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        linux-riscv@...ts.infradead.org
Subject: Re: [PATCH v4 1/2] dt-bindings: timer: thead,c900-aclint-mtimer:
 separate mtime and mtimecmp regs

Yo,

On Sat, Nov 18, 2023 at 03:10:26PM +0800, Inochi Amaoto wrote:
> The timer registers of aclint don't follow the clint layout and can
> be mapped on any different offset. As sg2042 uses separated timer
> and mswi for its clint, it should follow the aclint spec and have
> separated registers.
> 
> The previous patch introduced a new type of T-HEAD aclint timer which
> has clint timer layout. Although it has the clint timer layout, it
> should follow the aclint spec and uses the separated mtime and mtimecmp
> regs. So a ABI change is needed to make the timer fit the aclint spec.
> 
> To make T-HEAD aclint timer more closer to the aclint spec, use
> regs-names to represent the mtimecmp register, which can avoid hack
> for unsupport mtime register of T-HEAD aclint timer.
> 
> Signed-off-by: Inochi Amaoto <inochiama@...look.com>
> Fixes: 4734449f7311 ("dt-bindings: timer: Add Sophgo sg2042 CLINT timer")
> Link: https://lists.infradead.org/pipermail/opensbi/2023-October/005693.html
> Link: https://github.com/riscv/riscv-aclint/blob/main/riscv-aclint.adoc
> ---
>  .../timer/thead,c900-aclint-mtimer.yaml       | 42 ++++++++++++++++++-
>  1 file changed, 41 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/devicetree/bindings/timer/thead,c900-aclint-mtimer.yaml b/Documentation/devicetree/bindings/timer/thead,c900-aclint-mtimer.yaml
> index fbd235650e52..053488fb1286 100644
> --- a/Documentation/devicetree/bindings/timer/thead,c900-aclint-mtimer.yaml
> +++ b/Documentation/devicetree/bindings/timer/thead,c900-aclint-mtimer.yaml
> @@ -17,7 +17,20 @@ properties:
>        - const: thead,c900-aclint-mtimer
> 
>    reg:
> -    maxItems: 1
> +    oneOf:
> +      - items:
> +          - description: MTIME Registers
> +          - description: MTIMECMP Registers
> +      - items:
> +          - description: MTIMECMP Registers
> +
> +  reg-names:
> +    oneOf:
> +      - items:
> +          - const: mtime
> +          - const: mtimecmp
> +      - items:
> +          - const: mtimecmp
> 
>    interrupts-extended:
>      minItems: 1
> @@ -28,8 +41,34 @@ additionalProperties: false
>  required:
>    - compatible
>    - reg
> +  - reg-names
>    - interrupts-extended
> 
> +allOf:
> +  - if:
> +      properties:
> +        compatible:
> +          contains:
> +            const: thead,c900-aclint-mtimer

Is this being the c900 compatible correct? You mention in your commit
message that this split is done on the sg2042, but the rule is applied
here for any c900 series "aclint". Do we know if this is a sophgo
specific thing (or even sg2042 specific), or if it applies generally?

> +    then:
> +      properties:
> +        reg:
> +          items:
> +            - description: MTIMECMP Registers
> +        reg-names:
> +          items:
> +            - const: mtimecmp

> +    else:
> +      properties:
> +        reg:
> +          items:
> +            - description: MTIME Registers
> +            - description: MTIMECMP Registers
> +        reg-names:
> +          items:
> +            - const: mtime
> +            - const: mtimecmp

If it applies generally, I would probably just delete this, but unless
someone can confirm this to be general, I'd probably leave the else
clause and swap for the specific sg2042 compatible above.

Otherwise, this looks like a better fix than you had proposed before :)

Thanks,
Conor.

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