linux-kernel - Re: [PATCH v5 2/4] dt-bindings: riscv: Add Svade and Svadu Entries

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Date: Fri, 21 Jun 2024 11:11:56 +0100
From: Conor Dooley <conor.dooley@...rochip.com>
To: Andrew Jones <ajones@...tanamicro.com>
CC: Anup Patel <apatel@...tanamicro.com>, Conor Dooley <conor@...nel.org>,
	Yong-Xuan Wang <yongxuan.wang@...ive.com>, <linux-kernel@...r.kernel.org>,
	<linux-riscv@...ts.infradead.org>, <kvm-riscv@...ts.infradead.org>,
	<kvm@...r.kernel.org>, <alex@...ti.fr>, <greentime.hu@...ive.com>,
	<vincent.chen@...ive.com>, 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>,
	<devicetree@...r.kernel.org>
Subject: Re: [PATCH v5 2/4] dt-bindings: riscv: Add Svade and Svadu Entries

On Fri, Jun 21, 2024 at 10:33:03AM +0200, Andrew Jones wrote:
> On Thu, Jun 20, 2024 at 11:55:44AM GMT, Anup Patel wrote:
> > On Wed, Jun 5, 2024 at 10:25 PM Conor Dooley <conor@...nel.org> wrote:
> > >
> > > On Wed, Jun 05, 2024 at 08:15:08PM +0800, Yong-Xuan Wang wrote:
> > > > Add entries for the Svade and Svadu extensions to the riscv,isa-extensions
> > > > property.
> > > >
> > > > Signed-off-by: Yong-Xuan Wang <yongxuan.wang@...ive.com>
> > > > ---
> > > >  .../devicetree/bindings/riscv/extensions.yaml | 30 +++++++++++++++++++
> > > >  1 file changed, 30 insertions(+)
> > > >
> > > > diff --git a/Documentation/devicetree/bindings/riscv/extensions.yaml b/Documentation/devicetree/bindings/riscv/extensions.yaml
> > > > index 468c646247aa..1e30988826b9 100644
> > > > --- a/Documentation/devicetree/bindings/riscv/extensions.yaml
> > > > +++ b/Documentation/devicetree/bindings/riscv/extensions.yaml
> > > > @@ -153,6 +153,36 @@ properties:
> > > >              ratified at commit 3f9ed34 ("Add ability to manually trigger
> > > >              workflow. (#2)") of riscv-time-compare.
> > > >
> > > > +        - const: svade
> > > > +          description: |
> > > > +            The standard Svade supervisor-level extension for raising page-fault
> > > > +            exceptions when PTE A/D bits need be set as ratified in the 20240213
> > > > +            version of the privileged ISA specification.
> > > > +
> > > > +            Both Svade and Svadu extensions control the hardware behavior when
> > > > +            the PTE A/D bits need to be set. The default behavior for the four
> > > > +            possible combinations of these extensions in the device tree are:
> > > > +            1. Neither svade nor svadu in DT: default to svade.
> > >
> > > I think this needs to be expanded on, as to why nothing means svade.
> > 
> > Actually if both Svade and Svadu are not present in DT then
> > it is left to the platform and OpenSBI does nothing.
> 
> This is a good point, and maybe it's worth integrating something that
> states this case is technically unknown into the final text. (Even though
> historically this has been assumed to mean svade.)

If that is assumed to mean svade at the moment, then that's what it has
to mean going forwards also.

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