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

[Conor Dooley]

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@xxxxxxxxxxxxxxxx>
> Signed-off-by: Anup Patel <apatel@xxxxxxxxxxxxxxxx>
> Signed-off-by: Tomasz Jeznach <tjeznach@xxxxxxxxxxxx>
> ---
>  .../bindings/iommu/riscv,iommu.yaml           | 149 ++++++++++++++++++
>  MAINTAINERS                                   |   7 +
>  2 files changed, 156 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/iommu/riscv,iommu.yaml
> 
> 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@xxxxxxxxxxxx>
> +
> +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.

> +  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.

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