Re: [RESEND PATCH V3 1/2] dt-bindings: riscv: add mmu-supports-svpbmt for Svpbmt

[Anup Patel <anup@brainfault.org>]

On Mon, Oct 25, 2021 at 11:30 AM Guo Ren <guoren@kernel.org> wrote:
>
> On Mon, Oct 25, 2021 at 12:17 PM Anup Patel <anup@brainfault.org> wrote:
> >
> > On Mon, Oct 25, 2021 at 9:36 AM <wefu@redhat.com> wrote:
> > >
> > > From: Wei Fu <wefu@redhat.com>
> > >
> > > Previous patch has added svpbmt in arch/riscv and changed the
> > > DT mmu-type. Update dt-bindings related property here.
> > >
> > > Signed-off-by: Wei Fu <wefu@redhat.com>
> > > Co-developed-by: Guo Ren <guoren@kernel.org>
> > > Signed-off-by: Guo Ren <guoren@kernel.org>
> > > Cc: Anup Patel <anup@brainfault.org>
> > > Cc: Palmer Dabbelt <palmer@dabbelt.com>
> > > Cc: Rob Herring <robh+dt@kernel.org>
> > > ---
> > >  Documentation/devicetree/bindings/riscv/cpus.yaml | 5 +++++
> > >  1 file changed, 5 insertions(+)
> > >
> > > diff --git a/Documentation/devicetree/bindings/riscv/cpus.yaml b/Documentation/devicetree/bindings/riscv/cpus.yaml
> > > index e534f6a7cfa1..76f324d85e12 100644
> > > --- a/Documentation/devicetree/bindings/riscv/cpus.yaml
> > > +++ b/Documentation/devicetree/bindings/riscv/cpus.yaml
> > > @@ -59,6 +59,11 @@ properties:
> > >        - riscv,sv48
> > >        - riscv,none
> > >
> > > +  mmu-supports-svpbmt:
> > > +    description:
> > > +      Describes the CPU's mmu-supports-svpbmt support
> > > +    $ref: '/schemas/types.yaml#/definitions/phandle'
> >
> > There were various proposals from different folks in the previous
> > email threads.
> >
> > I think most of us were converging on:
> > 1) Don't modify "mmu-type" DT property for backward
> > compatibility
> I agree. FuWei has followed that in the patch.
>
> > 2) Add boolean DT property "riscv,svpmbt" under
> > "mmu" child DT node of each CPU DT node. Same will apply
> > to boolean DT property "riscv,svnapot" as well.
> We have various proposals here:
> @Philipp suggests firstly, but break the backward compatibility:
>  cpu@0 {
>     ...
>     mmu {
>        type = "riscv,sv39";
>        supports-svpbmt;
>        supports-svnapot;
>     };
>
> @guoren suggests reusing the mmu-type, but seems not clean.
> cpu@0 {
>    ...
>    mmu-type = "riscv,sv39,svpbmt,svnapot";
>
>
> @fuwei suggests simple name property in CPU section:
> cpu@0 {
>    ...
>    mmu-type = "riscv,sv39";
>    mmu-supports-svpbmt;
>    mmu-supports-svnapot;
>
> @Anup suggests:
> cpu@0 {
>    ...
>     mmu-type = "riscv,sv39";
>     mmu {
>        supports-svpbmt;
>        supports-svnapot;
>     };
>
> Any other suggestions? Thx.
>
> >
> > We also have bitmanip and vector broken down into smaller
> > extensions so grouping related extensions as separate DT node
> > under each CPU node will be more readable and easy to parse.
> Do you mean combine mmu extensions with them together?
> cpu@0 {
>     ...
>     extensions {
>         supports-svpbmt;
>         supports-svnapot;
>         supports-bitmanip;
>         supports-vector-v0p7;
>     };

I meant separate group nodes like this:

cpu@0 {
    ...
    mmu-type = "riscv,sv39";
    mmu { /* Only considered when mmu-type is present and mmu-type !=
"riscv,sv32" */
        riscv,svpmbt;
        riscv,svnapot;
    };

    bitmanip { /* Only considered when "B" is present in the ISA string */
        ...
    };

   vector { /* Only considered when "V" is present in the ISA string */
       ...
   };
    ...
};

Regards,
Anup

>
> >
> > Regards,
> > Anup
> >
> > > +
> > >    riscv,isa:
> > >      description:
> > >        Identifies the specific RISC-V instruction set architecture
> > > --
> > > 2.25.4
> > >
>
>
>
> --
> Best Regards
>  Guo Ren
>
> ML: https://lore.kernel.org/linux-csky/