Re: [PATCH v2] dt-bindings: iommu: riscv: Add bindings for Tenstorrent RISC-V IOMMU

[Drew Fustini <fustini@kernel.org>]

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On Wed, May 20, 2026 at 05:17:41PM +0100, Conor Dooley wrote:

Thanks for the review...

> On Tue, May 19, 2026 at 11:16:28PM -0700, Drew Fustini wrote:
> > From: Nicholas Piggin <npiggin@gmail.com>
> > 
> > Extend the binding to cover details specific to the Tenstorrent RISC-V
> > IOMMU. In particular, a second register range is added which contains
> > M-privileged registers, e.g., PMAs and PMPs.
> > 
> > The RISC-V spec S-privileged registers remain in the first register
> > range and are compatible with "riscv,iommu" so the Linux driver does not
> > notice any difference, but the binding will be used by OpenSBI and
> > potentially other M-mode software.
> > 
> > Reviewed-by: Joel Stanley <joel@jms.id.au>
> > Acked-by: Joerg Roedel <joerg.roedel@amd.com>
> > Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
> > [fustini: fix dt_binding_check errors]
> > Signed-off-by: Drew Fustini <fustini@kernel.org>
> > ---
> > v2 changes:
> > - Fix dt_binding_check errors
> > - Add the Acked-by: from Joerg
> > - Drop RFC prefix
> > 
> > Link to v1:
> > https://lore.kernel.org/lkml/20260310003850.3837030-1-npiggin@gmail.com/
> > 
> >  .../bindings/iommu/riscv,iommu.yaml           | 62 ++++++++++++++++---
> >  1 file changed, 55 insertions(+), 7 deletions(-)
> > 
> > diff --git a/Documentation/devicetree/bindings/iommu/riscv,iommu.yaml b/Documentation/devicetree/bindings/iommu/riscv,iommu.yaml
> > index d4838c3b3741..5aad8cf67840 100644
> > --- a/Documentation/devicetree/bindings/iommu/riscv,iommu.yaml
> > +++ b/Documentation/devicetree/bindings/iommu/riscv,iommu.yaml
> > @@ -32,22 +32,35 @@ properties:
> >    # should be specified along with 'reg' property providing MMIO location.
> >    compatible:
> >      oneOf:
> > -      - items:
> > +      - description: Platform (non-PCIe) IOMMU implementations
> > +        items:
> >            - enum:
> >                - qemu,riscv-iommu
> >            - const: riscv,iommu
> > -      - items:
> > +      - description: PCIe IOMMU implementations
> > +        items:
> >            - enum:
> >                - pci1efd,edf1
> >            - const: riscv,pci-iommu
> > +      - description: Tenstorrent IOMMUs implementing "riscv,iommu"
> > +        items:
> > +          - enum:
> > +              - tenstorrent,riscv-iommu
> > +          - const: riscv,iommu
> 
> You should be able to put this into the enum alongside the qemu
> compatible, right?

Good point, I'll move tenstorrent,riscv-iommu to the enum with
qemu,riscv-iommu.

> > +allOf:
> > +  - if:
> > +      properties:
> > +        compatible:
> > +          contains:
> > +            enum:
> > +              - tenstorrent,riscv-iommu
> > +    then:
> > +      properties:
> > +        reg:
> 
> > +          items:
> > +            - description: IOMMU base registers
> > +            - description: Tenstorrent IOMMU machine mode registers.
> 
> Should this also have minItems: 2?

I think items: with 2 items implies minItems: 2 but I see your later
point about the description and names don't belong in the allOf: block.

> 
> > +        reg-names:
> 
> > +          items:
> > +            - const: base
> > +            - const: machine
> > +              description:
> > +                Region containing platform specific MMRs for machine-mode
> > +                configuration, such as PMA and PMP registers.
> 
> And this you should replace with minItems: 2 or delete. The reg property
> is where your description here belongs and all the names do here is
> re-list what's available outside the condition.

Ah, so I just have minItems: 2 here and rely on the reg: section to have
the descriptions.

> > +  - |+
> > +    /* Example 5 (Tenstorrent IOMMU device with MSIs) */
> > +    iommu5: iommu@d2020000 {
> > +        compatible = "tenstorrent,riscv-iommu", "riscv,iommu";
> > +        reg = <0xd2020000 0x10000 0xaa000000 0x10000>;
> 
> This is not the correct format for multiple reg properties. Hint: you're
> missing ">, <".

Thanks, I'll fix that.

-Drew

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