[PATCH v5 2/4] dt-bindings: riscv: Add Svade and Svadu Entries

[Yong-Xuan Wang]

On Thu, Jun 6, 2024 at 12:55 AM Conor Dooley <conor at kernel.org> wrote:
>
> On Wed, Jun 05, 2024 at 08:15:08PM +0800, Yong-Xuan Wang wrote:
> > Add entries for the Svade and Svadu extensions to the riscv,isa-extensions
> > property.
> >
> > Signed-off-by: Yong-Xuan Wang <yongxuan.wang at sifive.com>
> > ---
> >  .../devicetree/bindings/riscv/extensions.yaml | 30 +++++++++++++++++++
> >  1 file changed, 30 insertions(+)
> >
> > diff --git a/Documentation/devicetree/bindings/riscv/extensions.yaml b/Documentation/devicetree/bindings/riscv/extensions.yaml
> > index 468c646247aa..1e30988826b9 100644
> > --- a/Documentation/devicetree/bindings/riscv/extensions.yaml
> > +++ b/Documentation/devicetree/bindings/riscv/extensions.yaml
> > @@ -153,6 +153,36 @@ properties:
> >              ratified at commit 3f9ed34 ("Add ability to manually trigger
> >              workflow. (#2)") of riscv-time-compare.
> >
> > +        - const: svade
> > +          description: |
> > +            The standard Svade supervisor-level extension for raising page-fault
> > +            exceptions when PTE A/D bits need be set as ratified in the 20240213
> > +            version of the privileged ISA specification.
> > +
> > +            Both Svade and Svadu extensions control the hardware behavior when
> > +            the PTE A/D bits need to be set. The default behavior for the four
> > +            possible combinations of these extensions in the device tree are:
> > +            1. Neither svade nor svadu in DT: default to svade.
>
> I think this needs to be expanded on, as to why nothing means svade.
>
> > +            2. Only svade in DT: use svade.
>
> That's a statement of the obvious, right?
>
> > +            3. Only svadu in DT: use svadu.
>
> This is not relevant for Svade.
>
> > +            4. Both svade and svadu in DT: default to svade (Linux can switch to
> > +               svadu once the SBI FWFT extension is available).
>
> "The privilege level to which this devicetree has been provided can switch to
> Svadu if the SBI FWFT extension is available".
>
> > +        - const: svadu
> > +          description: |
> > +            The standard Svadu supervisor-level extension for hardware updating
> > +            of PTE A/D bits as ratified at commit c1abccf ("Merge pull request
> > +            #25 from ved-rivos/ratified") of riscv-svadu.
> > +
> > +            Both Svade and Svadu extensions control the hardware behavior when
> > +            the PTE A/D bits need to be set. The default behavior for the four
> > +            possible combinations of these extensions in the device tree are:
>
> @Anup/Drew/Alex, are we missing some wording in here about it only being
> valid to have Svadu in isolation if the provider of the devicetree has
> actually turned on Svadu? The binding says "the default behaviour", but
> it is not the "default" behaviour, the behaviour is a must AFAICT. If
> you set Svadu in isolation, you /must/ have turned it on. If you set
> Svadu and Svade, you must have Svadu turned off?
>
> > +            1. Neither svade nor svadu in DT: default to svade.
> > +            2. Only svade in DT: use svade.
>
> These two are not relevant to Svadu, I'd leave them out.
>
> > +            3. Only svadu in DT: use svadu.
>
> Again, statement of the obvious?
>
> > +            4. Both svade and svadu in DT: default to svade (Linux can switch to
> > +               svadu once the SBI FWFT extension is available).
>
> Same here as in the Svade entry.
>
> Thanks,
> Conor.
>

Hi Conor,

I will update the description. Thank you!

Regards,
Yong-Xuan