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

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Date: Mon, 10 Jun 2024 20:28:22 +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 Mon, Jun 10, 2024 at 09:38:06AM -0700, Charlie Jenkins wrote:
> 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!

And in this case dtbs_check would also complain about riscv,vlenb being
undocumented - and complain about thead,vlenb not being a permitted cpu
property either.

Thanks,
Conor.

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