Re: [RFC PATCH 2/3] dt-bindings: riscv: Add Worlds per-hart properties

[Conor Dooley]

On Fri, Jun 26, 2026 at 07:47:31PM +0800, Yu-Chien Peter Lin wrote:
> Hi Conor,
> 
> On Mon, Jun 22, 2026 at 06:12:47PM +0100, Conor Dooley wrote:
> > On Fri, Jun 19, 2026 at 06:58:33PM +0800, Yu-Chien Peter Lin wrote:
> > > Add per-hart DT properties for RISC-V Worlds architecture:
> > > riscv,pmwid, riscv,pmwidlist, and riscv,pmlwidlist. These
> > > platform-defined values are primarily used by M-mode firmware
> > > to configure World ID CSRs and restrict WID usage across
> > > privilege levels.
> > > 
> > > Signed-off-by: Yu-Chien Peter Lin <peter.lin@xxxxxxxxxx>
> > > ---
> > >  .../devicetree/bindings/riscv/cpus.yaml       | 21 +++++
> > >  .../devicetree/bindings/riscv/worlds.yaml     | 77 +++++++++++++++++++
> > >  2 files changed, 98 insertions(+)
> > >  create mode 100644 Documentation/devicetree/bindings/riscv/worlds.yaml
> > > 
> > > diff --git a/Documentation/devicetree/bindings/riscv/cpus.yaml b/Documentation/devicetree/bindings/riscv/cpus.yaml
> > > index 5feeb2203050..4b5778b6d3e7 100644
> > > --- a/Documentation/devicetree/bindings/riscv/cpus.yaml
> > > +++ b/Documentation/devicetree/bindings/riscv/cpus.yaml
> > > @@ -26,6 +26,7 @@ description: |
> > >  allOf:
> > >    - $ref: /schemas/cpu.yaml#
> > >    - $ref: extensions.yaml
> > > +  - $ref: worlds.yaml
> > >    - if:
> > >        not:
> > >          properties:
> > > @@ -120,11 +121,31 @@ properties:
> > >        thead systems where the vector register length is not identical on all harts, or
> > >        the vlenb CSR is not available.
> > >  
> > > +  riscv,pmwid:
> > > +    $ref: /schemas/types.yaml#/definitions/uint32
> > > +    description:
> > > +      Platform-defined M-mode World ID (WID) assigned to this hart.
> > > +    minimum: 0
> > > +    maximum: 63
> > > +
> > > +  riscv,pmwidlist:
> > > +    $ref: /schemas/types.yaml#/definitions/uint64
> > > +    description:
> > > +      Platform-defined bitmap of M-mode World IDs (WIDs) that this hart may use.
> > 
> > I don't understand what the difference is between this property and the
> > one before it are.
> > Is this one meant to be used by m-mode software to then select one which
> > will appear in riscv,pmwid?
> 
> pmwid (single value) is the reset default, while pmwidlist (bitmap)
> defines the allowed set. The root-of-trust M-mode software may select
> an allowed value from the pmwidlist and write it to the mwid CSR.

I don't understand the point of the property then. If it is the reset
default, just read it out of the register?
Unless I am missing something, it's useless to s-mode because it may
not be what m-mode chose and useless to m-mode that has access to
the csr.

Cheers,
Conor.

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