Re: [PATCH V4 1/2] dt-bindings: riscv: add MMU Standard Extensions support for Svpbmt

[Heiko Stübner]

Am Montag, 29. November 2021, 09:54:39 CET schrieb Heinrich Schuchardt:
> On 11/29/21 02:40, wefu@xxxxxxxxxx wrote:
> > From: Wei Fu <wefu@xxxxxxxxxx>
> > 
> > Previous patch has added svpbmt in arch/riscv and add "riscv,svpmbt"
> > in the DT mmu node. Update dt-bindings related property here.
> > 
> > Signed-off-by: Wei Fu <wefu@xxxxxxxxxx>
> > Co-developed-by: Guo Ren <guoren@xxxxxxxxxx>
> > Signed-off-by: Guo Ren <guoren@xxxxxxxxxx>
> > Cc: Anup Patel <anup@xxxxxxxxxxxxxx>
> > Cc: Palmer Dabbelt <palmer@xxxxxxxxxxx>
> > Cc: Rob Herring <robh+dt@xxxxxxxxxx>
> > ---
> >   Documentation/devicetree/bindings/riscv/cpus.yaml | 10 ++++++++++
> >   1 file changed, 10 insertions(+)
> > 
> > diff --git a/Documentation/devicetree/bindings/riscv/cpus.yaml b/Documentation/devicetree/bindings/riscv/cpus.yaml
> > index aa5fb64d57eb..9ff9cbdd8a85 100644
> > --- a/Documentation/devicetree/bindings/riscv/cpus.yaml
> > +++ b/Documentation/devicetree/bindings/riscv/cpus.yaml
> > @@ -63,6 +63,16 @@ properties:
> >         - riscv,sv48
> >         - riscv,none
> >   
> > +  mmu:
> 
> Shouldn't we keep the items be in alphabetic order, i.e. mmu before 
> mmu-type?
> 
> > +    description:
> > +      Describes the CPU's MMU Standard Extensions support.
> > +      These values originate from the RISC-V Privileged
> > +      Specification document, available from
> > +      https://riscv.org/specifications/
> > +    $ref: '/schemas/types.yaml#/definitions/string'
> > +    enum:
> > +      - riscv,svpmbt
> 
> The privileged specification has multiple MMU related extensions: 
> Svnapot, Svpbmt, Svinval. Shall they all be modeled in this enum?

I remember in some earlier version some way back there was the
suggestion of using a sub-node instead and then adding boolean
properties for the supported extensions.

Aka something like
	mmu {
		riscv,svpbmt;	
	};

Which I guess would be a lot nicer. Also right now there is string-
comparison done on the code side, which would look way easier
when just looking for booleans in the dt instead.

Also isn't an enum a "one-of" selection, so wouldn't work directly
for multiple extensions?


Heiko


> 
> Best regards
> 
> Heinrich
> 
> > +
> >     riscv,isa:
> >       description:
> >         Identifies the specific RISC-V instruction set architecture
> > 
> 
> 
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