linux-kernel - Re: [PATCH v1] dt-bindings: riscv: explicitly mention assumption of Zicsr & Zifencei support

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Date:   Mon, 01 May 2023 17:00:15 -0700 (PDT)
From:   Palmer Dabbelt <palmer@...belt.com>
To:     Conor Dooley <conor.dooley@...rochip.com>
CC:     Conor Dooley <conor@...nel.org>,
        Conor Dooley <conor.dooley@...rochip.com>, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org,
        Paul Walmsley <paul.walmsley@...ive.com>,
        linux-riscv@...ts.infradead.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject:     Re: [PATCH v1] dt-bindings: riscv: explicitly mention assumption of Zicsr & Zifencei support

On Thu, 27 Apr 2023 03:43:42 PDT (-0700), Conor Dooley wrote:
> The dt-binding was defined before the extraction of csr access and
> fence.i into their own extensions, and thus the presence of the I
> base extension implies Zicsr and Zifencei.
> There's no harm in adding them obviously, but for backwards
> compatibility with DTs that existed prior to that extraction, software
> is unable to differentiate between "i" and "i_zicsr_zifencei" without
> any further information.
>
> Signed-off-by: Conor Dooley <conor.dooley@...rochip.com>
> ---
> CC: Conor Dooley <conor@...nel.org>
> CC: Rob Herring <robh+dt@...nel.org>
> CC: Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>
> CC: Paul Walmsley <paul.walmsley@...ive.com>
> CC: Palmer Dabbelt <palmer@...belt.com>
> CC: linux-riscv@...ts.infradead.org
> CC: devicetree@...r.kernel.org
> CC: linux-kernel@...r.kernel.org
> ---
>  Documentation/devicetree/bindings/riscv/cpus.yaml | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/Documentation/devicetree/bindings/riscv/cpus.yaml b/Documentation/devicetree/bindings/riscv/cpus.yaml
> index 4c7ce4a37052..a93bc7eae928 100644
> --- a/Documentation/devicetree/bindings/riscv/cpus.yaml
> +++ b/Documentation/devicetree/bindings/riscv/cpus.yaml
> @@ -85,6 +85,12 @@ properties:
>        User-Level ISA document, available from
>        https://riscv.org/specifications/
>
> +      Due to revisions of the ISA specification, some deviations
> +      have arisen over time.
> +      Notably, riscv,isa was defined prior to the creation of the
> +      Zicsr and Zifencei extensions and thus "i" implies
> +      "zicsr_zifencei".

also Zihpm and Zicntr.  I'm going to put this one on for-next, though.

Thanks!

> +
>        While the isa strings in ISA specification are case
>        insensitive, letters in the riscv,isa string must be all
>        lowercase to simplify parsing.