linux-kernel - Re: [PATCH 02/13] dt-bindings: thead: add a vlen register length property

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Message-ID: <20240610-unaltered-crazily-5b63e224d633@spud>
Date: Mon, 10 Jun 2024 17:29:23 +0100
From: Conor Dooley <conor@...nel.org>
To: Charlie Jenkins <charlie@...osinc.com>
Cc: Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Paul Walmsley <paul.walmsley@...ive.com>,
	Palmer Dabbelt <palmer@...belt.com>,
	Albert Ou <aou@...s.berkeley.edu>,
	Jisheng Zhang <jszhang@...nel.org>, Chen-Yu Tsai <wens@...e.org>,
	Jernej Skrabec <jernej.skrabec@...il.com>,
	Samuel Holland <samuel@...lland.org>,
	Jonathan Corbet <corbet@....net>, Shuah Khan <shuah@...nel.org>,
	Guo Ren <guoren@...nel.org>, Evan Green <evan@...osinc.com>,
	Andy Chiu <andy.chiu@...ive.com>, linux-riscv@...ts.infradead.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-sunxi@...ts.linux.dev, linux-doc@...r.kernel.org,
	linux-kselftest@...r.kernel.org
Subject: Re: [PATCH 02/13] dt-bindings: thead: add a vlen register length
 property

On Sun, Jun 09, 2024 at 09:45:07PM -0700, Charlie Jenkins wrote:
> Add a property analogous to the vlenb CSR so that software can detect
> the vector length of each CPU prior to it being brought online.
> Currently software has to assume that the vector length read from the
> boot CPU applies to all possible CPUs. On T-Head CPUs implementing
> pre-ratification vector, reading the th.vlenb CSR may produce an illegal
> instruction trap, so this property is required on such systems.
> 
> Signed-off-by: Charlie Jenkins <charlie@...osinc.com>
> ---
>  Documentation/devicetree/bindings/riscv/thead.yaml | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/riscv/thead.yaml b/Documentation/devicetree/bindings/riscv/thead.yaml
> index 301912dcd290..5e578df36ac5 100644
> --- a/Documentation/devicetree/bindings/riscv/thead.yaml
> +++ b/Documentation/devicetree/bindings/riscv/thead.yaml
> @@ -28,6 +28,13 @@ properties:
>            - const: sipeed,lichee-module-4a
>            - const: thead,th1520
>  
> +thead,vlenb:

This needs to move back into cpus.yaml, this file documents root node
compatibles (boards and socs etc) and is not for CPUs. If you want to
restrict this to T-Head CPUs only, it must be done in cpus.yaml with
a conditional `if: not: ... then: properties: thead,vlenb: false`.

Please test your bindings.

Thanks,
Conor.

> +  $ref: /schemas/types.yaml#/definitions/uint32
> +  description:
> +    VLEN/8, the vector register length in bytes. This property is required in
> +    systems where the vector register length is not identical on all harts, or
> +    the vlenb CSR is not available.
> +
>  additionalProperties: true
>  
>  ...
> 
> -- 
> 2.44.0
> 

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