Re: [PATCH] riscv: Add RISC-V svpbmt extension

[Nick Kossifidis]

Στις 2021-09-23 12:37, Anup Patel έγραψε:
> On Thu, Sep 23, 2021 at 2:55 PM Nick Kossifidis <mick@xxxxxxxxxxxx> 
> wrote:
> > Hello Guo,
> >
> > Στις 2021-09-23 10:27, guoren@xxxxxxxxxx έγραψε:
> > diff --git a/Documentation/devicetree/bindings/riscv/cpus.yaml
> > b/Documentation/devicetree/bindings/riscv/cpus.yaml
> > index e534f6a7cfa1..1825cd8db0de 100644
> > --- a/Documentation/devicetree/bindings/riscv/cpus.yaml
> > +++ b/Documentation/devicetree/bindings/riscv/cpus.yaml
> > @@ -56,7 +56,9 @@ properties:
> >       enum:
> >         - riscv,sv32
> >         - riscv,sv39
> > +      - riscv,sv39,svpbmt
> >         - riscv,sv48
> > +      - riscv,sv48,svpbmt
> >         - riscv,none
> >
> > Isn't svpbmt orthogonal to the mmu type ? It's a functionality that 
> > can
> > be present on either sv39/48/57 so why not have another "svpbmt"
> > property directly on the cpu node ?
>
> Actually, "mmu-type" would be a good place because it's page based
> memory attribute and paging can't exist without mmu translation mode.
>
> Also, "svpmbt" is indeed a CPU property so has to be feature individual
> CPU node. Hypothetically, a heterogeneous system is possible where
> some CPUs have "svpmbt" and some CPUs don't have "svpmbt". For
> example, a future FUxxx SoC might have a E-core and few S-cores
> where S-cores have Svpmbt whereas E-core does not have Svpmbt
> because it's an embedded core.

I should say cpuX node, not the root /cpu node. We can have an svpbmt 
property in the same way we have an mmu-type property.

Regards,
Nick