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

[Philipp Tomsich]

On Mon, 25 Oct 2021 at 08:08, Anup Patel <anup@xxxxxxxxxxxxxx> wrote:
>
> On Mon, Oct 25, 2021 at 11:30 AM Guo Ren <guoren@xxxxxxxxxx> wrote:
> >
> > On Mon, Oct 25, 2021 at 12:17 PM Anup Patel <anup@xxxxxxxxxxxxxx> wrote:
> > >
> > > On Mon, Oct 25, 2021 at 9:36 AM <wefu@xxxxxxxxxx> wrote:
> > > >
> > > > From: Wei Fu <wefu@xxxxxxxxxx>
> > > >
> > > > 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@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 | 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 */
>         ...
>     };

Please disregard this comment regarding bitmanip/B.
The B bit in the misa CSR is not used for any signalling regarding
Zb[abcs] (or the other Zb-extensions), so this entire node is not
needed and B in the ISA string is not related to any of the Zb*
extensions).
All Zb* extensions are directly visible from 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/