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

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Message-ID: <Zmcr7pP+XEWHYTsy@ghost>
Date: Mon, 10 Jun 2024 09:38:06 -0700
From: Charlie Jenkins <charlie@...osinc.com>
To: Conor Dooley <conor@...nel.org>
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 Mon, Jun 10, 2024 at 05:29:23PM +0100, Conor Dooley wrote:
> 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.

Now that I know `make dt_binding_check` exists I will use that in the
future!

- Charlie

> 
> 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
> >