linux-kernel - Re: [PATCH 1/3] dt-bindings: riscv: Add Supm extension description

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Message-ID: <20260123-regime-example-c53814f85bad@spud>
Date: Fri, 23 Jan 2026 17:24:09 +0000
From: Conor Dooley <conor@...nel.org>
To: Guodong Xu <guodong@...cstar.com>
Cc: Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Samuel Holland <samuel.holland@...ive.com>,
	Heinrich Schuchardt <heinrich.schuchardt@...onical.com>,
	Paul Walmsley <pjw@...nel.org>, Palmer Dabbelt <palmer@...belt.com>,
	Albert Ou <aou@...s.berkeley.edu>, Alexandre Ghiti <alex@...ti.fr>,
	Evan Green <evan@...osinc.com>,
	Andrew Jones <ajones@...tanamicro.com>,
	Paul Walmsley <paul.walmsley@...ive.com>,
	devicetree@...r.kernel.org, linux-riscv@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] dt-bindings: riscv: Add Supm extension description

On Fri, Jan 23, 2026 at 07:29:52AM +0800, Guodong Xu wrote:
> On Fri, Jan 23, 2026 at 2:52 AM Conor Dooley <conor@...nel.org> wrote:
> >
> > On Fri, Jan 16, 2026 at 10:10:31AM +0800, Guodong Xu wrote:
> > > Add description for the Supm extension. Supm indicates support for pointer
> > > masking in user mode. Supm is mandatory for RVA23S64.
> > >
> > > The Supm extension is ratified in commit d70011dde6c2 ("Update to ratified
> > > state") of riscv-j-extension.
> > >
> > > Signed-off-by: Guodong Xu <guodong@...cstar.com>
> > > ---
> > >  Documentation/devicetree/bindings/riscv/extensions.yaml | 17 +++++++++++++++++
> > >  1 file changed, 17 insertions(+)
> > >
> > > diff --git a/Documentation/devicetree/bindings/riscv/extensions.yaml b/Documentation/devicetree/bindings/riscv/extensions.yaml
> > > index 4ffd61926505..1922dff03787 100644
> > > --- a/Documentation/devicetree/bindings/riscv/extensions.yaml
> > > +++ b/Documentation/devicetree/bindings/riscv/extensions.yaml
> > > @@ -262,6 +262,23 @@ properties:
> > >              ratified in RISC-V Profiles Version 1.0, with commit b1d806605f87
> > >              ("Updated to ratified state.")
> > >
> > > +        - const: supm
> > > +          description: |
> > > +            The standard Supm extension for pointer masking support in user
> > > +            mode (U-mode) as ratified at commit d70011dde6c2 ("Update to
> > > +            ratified state") of riscv-j-extension.
> > > +
> > > +            Supm represents a combination of underlying hardware capability
> > > +            (Smnpm or Ssnpm), U-mode consumer privilege level, and M/S-mode
> >
> > Should we therefore make this require that Smnpm or Ssnpm are present?
> 
> I'm not sure. Would U-mode DTBs typically omit the privileged extensions like
> Smnpm/Ssnpm, making such a dependency impractical?

I don't actually know of any u-mode software that uses a devicetree, but
my guy feeling is that people won't trim out the lower-priv mode things
because they might want/need to know if those features are available on the
platform.

> > > +            software configuration that enables pointer masking for U-mode.
> > > +
> > > +            DO NOT include this property in device trees targeting privileged
> > > +            system software (S-mode or M-mode).
> > > +
> > > +            This property is only appropriate in device trees provided to
> > > +            U-mode software where the next-higher-privilege-mode supports
> > > +            Smnpm or Ssnpm and enables it for U-mode.
> > > +
> > >          - const: svade
> > >            description: |
> > >              The standard Svade supervisor-level extension for SW-managed PTE A/D
> > >
> > > --
> > > 2.43.0
> > >

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