Re: [PATCH v2 4/6] dt-bindings: Add RISC-V misaligned access performance

From: Conor Dooley <conor@kernel.org>
To: Evan Green <evan@rivosinc.com>
Cc: Palmer Dabbelt <palmer@rivosinc.com>,
	vineetg@rivosinc.com, heiko@sntech.de, slewis@rivosinc.com,
	Albert Ou <aou@eecs.berkeley.edu>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Rob Herring <robh+dt@kernel.org>,
	devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-riscv@lists.infradead.org
Subject: Re: [PATCH v2 4/6] dt-bindings: Add RISC-V misaligned access performance
Date: Tue, 14 Feb 2023 21:26:16 +0000	[thread overview]
Message-ID: <Y+v8eNlcG+jbB2oy@spud> (raw)
In-Reply-To: <20230206201455.1790329-5-evan@rivosinc.com>

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On Mon, Feb 06, 2023 at 12:14:53PM -0800, Evan Green wrote:
> From: Palmer Dabbelt <palmer@rivosinc.com>
> 
> This key allows device trees to specify the performance of misaligned
> accesses to main memory regions from each CPU in the system.
> 
> Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
> Signed-off-by: Evan Green <evan@rivosinc.com>
> ---
> 
> (no changes since v1)
> 
>  Documentation/devicetree/bindings/riscv/cpus.yaml | 15 +++++++++++++++
>  1 file changed, 15 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/riscv/cpus.yaml b/Documentation/devicetree/bindings/riscv/cpus.yaml
> index c6720764e765..2c09bd6f2927 100644
> --- a/Documentation/devicetree/bindings/riscv/cpus.yaml
> +++ b/Documentation/devicetree/bindings/riscv/cpus.yaml
> @@ -85,6 +85,21 @@ properties:
>      $ref: "/schemas/types.yaml#/definitions/string"
>      pattern: ^rv(?:64|32)imaf?d?q?c?b?v?k?h?(?:_[hsxz](?:[a-z])+)*$
>  
> +  riscv,misaligned-access-performance:
> +    description:
> +      Identifies the performance of misaligned memory accesses to main memory
> +      regions.  There are three flavors of unaligned access performance: "emulated"

Is the performance: emulated the source of the dt_binding_check issues?
And the fix is as simple as:
-    description:
+    description: |
?

> +      means that misaligned accesses are emulated via software and thus
> +      extremely slow, "slow" means that misaligned accesses are supported by
> +      hardware but still slower that aligned accesses sequences, and "fast"
> +      means that misaligned accesses are as fast or faster than the
> +      cooresponding aligned accesses sequences.
> +    $ref: "/schemas/types.yaml#/definitions/string"
> +    enum:
> +      - emulated
> +      - slow
> +      - fast
> +
>    # RISC-V requires 'timebase-frequency' in /cpus, so disallow it here
>    timebase-frequency: false
>  
> -- 
> 2.25.1
> 

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