linux-kernel - Re: [PATCH v2 1/7] dt-bindings: iommu: riscv: Add bindings for RISC-V IOMMU

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Date: Wed, 24 Apr 2024 15:37:14 -0700
From: Tomasz Jeznach <tjeznach@...osinc.com>
To: Conor Dooley <conor@...nel.org>
Cc: Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>, 
	Robin Murphy <robin.murphy@....com>, Paul Walmsley <paul.walmsley@...ive.com>, 
	Palmer Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>, 
	Anup Patel <apatel@...tanamicro.com>, Sunil V L <sunilvl@...tanamicro.com>, 
	Nick Kossifidis <mick@....forth.gr>, Sebastien Boeuf <seb@...osinc.com>, Rob Herring <robh+dt@...nel.org>, 
	Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, devicetree@...r.kernel.org, 
	iommu@...ts.linux.dev, linux-riscv@...ts.infradead.org, 
	linux-kernel@...r.kernel.org, linux@...osinc.com
Subject: Re: [PATCH v2 1/7] dt-bindings: iommu: riscv: Add bindings for RISC-V IOMMU

On Thu, Apr 18, 2024 at 10:04 AM Conor Dooley <conor@...nel.org> wrote:
>
> On Thu, Apr 18, 2024 at 09:32:19AM -0700, Tomasz Jeznach wrote:
> > Add bindings for the RISC-V IOMMU device drivers.
> >
> > Co-developed-by: Anup Patel <apatel@...tanamicro.com>
> > Signed-off-by: Anup Patel <apatel@...tanamicro.com>
> > Signed-off-by: Tomasz Jeznach <tjeznach@...osinc.com>
> > ---
> >  .../bindings/iommu/riscv,iommu.yaml           | 149 ++++++++++++++++++
> >  MAINTAINERS                                   |   7 +
> >  2 files changed, 156 insertions(+)
> >  create mode 100644 Documentation/devicetree/bindings/iommu/riscv,iommuyaml
> >
> > diff --git a/Documentation/devicetree/bindings/iommu/riscv,iommu.yaml b/Documentation/devicetree/bindings/iommu/riscv,iommu.yaml
> > new file mode 100644
> > index 000000000000..d6522ddd43fa
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/iommu/riscv,iommu.yaml
> > @@ -0,0 +1,149 @@
> > +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> > +%YAML 1.2
> > +---
> > +$id: http://devicetree.org/schemas/iommu/riscv,iommu.yaml#
> > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > +
> > +title: RISC-V IOMMU Architecture Implementation
> > +
> > +maintainers:
> > +  - Tomasz Jeznach <tjeznach@...osinc.com>
> > +
> > +description: |+
>
> FYI, the + here is probably not needed.
>
> > +  The RISC-V IOMMU provides memory address translation and isolation for
> > +  input and output devices, supporting per-device translation context,
> > +  shared process address spaces including the ATS and PRI components of
> > +  the PCIe specification, two stage address translation and MSI remapping.
> > +  It supports identical translation table format to the RISC-V address
> > +  translation tables with page level access and protection attributes.
> > +  Hardware uses in-memory command and fault reporting queues with wired
> > +  interrupt or MSI notifications.
> > +
> > +  Visit https://github.com/riscv-non-isa/riscv-iommu for more details.
> > +
> > +  For information on assigning RISC-V IOMMU to its peripheral devices,
> > +  see generic IOMMU bindings.
> > +
> > +properties:
> > +  # For PCIe IOMMU hardware compatible property should contain the vendor
> > +  # and device ID according to the PCI Bus Binding specification.
> > +  # Since PCI provides built-in identification methods, compatible is not
> > +  # actually required. For non-PCIe hardware implementations 'riscv,iommu'
> > +  # should be specified along with 'reg' property providing MMIO location.
>
> I dunno, I'd like to see soc-specific compatibles for implementations of
> the RISC-V IOMMU. If you need a DT compatible for use in QEMU, I'd
> suggest doing what was done for the aplic and having a dedicated
> compatible for that and disallow having "riscv,iommu" in isolation.
>

Makes sense.  Will update to something like below:
  compatible:
    oneOf:
      - items:
          - enum:
              - qemu,iommu
          - const: riscv,iommu
      - items:
          - enum:
              - pci1efd,edf1
          - const: riscv,pci-iommu

> > +  compatible:
> > +    oneOf:
> > +      - items:
> > +          - const: riscv,pci-iommu
> > +          - const: pci1efd,edf1
> > +      - items:
> > +          - const: pci1efd,edf1
>
> Why are both versions allowed? If the former is more understandable,
> can't we just go with that?
>
> > +      - items:
> > +          - const: riscv,iommu
>
> Other than the compatible setup I think this is pretty decent though,
> Conor.

ACK to other comments,

Thanks for the review,
- Tomasz