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

[Guo Ren <guoren@kernel.org>]

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;
    };

>
> 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/