Re: [PATCH 03/11] dt-bindings: Add RISC-V IOMMU bindings

[Anup Patel]

On Mon, Jul 24, 2023 at 1:33 PM Zong Li <zong.li@xxxxxxxxxx> wrote:
>
> On Thu, Jul 20, 2023 at 3:35 AM Tomasz Jeznach <tjeznach@xxxxxxxxxxxx> wrote:
> >
> > From: Anup Patel <apatel@xxxxxxxxxxxxxxxx>
> >
> > We add DT bindings document for RISC-V IOMMU platform and PCI devices
> > defined by the RISC-V IOMMU specification.
> >
> > Signed-off-by: Anup Patel <apatel@xxxxxxxxxxxxxxxx>
> > ---
> >  .../bindings/iommu/riscv,iommu.yaml           | 146 ++++++++++++++++++
> >  1 file changed, 146 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..8a9aedb61768
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/iommu/riscv,iommu.yaml
> > @@ -0,0 +1,146 @@
> > +# 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 Implementation
> > +
> > +maintainers:
> > +  - Tomasz Jeznach <tjeznach@xxxxxxxxxxxx>
> > +
> > +description:
> > +  The RISC-V IOMMU specificaiton defines an IOMMU for RISC-V platforms
> > +  which can be a regular platform device or a PCI device connected to
> > +  the host root port.
> > +
> > +  The RISC-V IOMMU provides two stage translation, device directory table,
> > +  command queue and fault reporting as wired interrupt or MSIx event for
> > +  both PCI and platform devices.
> > +
> > +  Visit https://github.com/riscv-non-isa/riscv-iommu for more details.
> > +
> > +properties:
> > +  compatible:
> > +    oneOf:
> > +      - description: RISC-V IOMMU as a platform device
> > +        items:
> > +          - enum:
> > +              - vendor,chip-iommu
> > +          - const: riscv,iommu
> > +
> > +      - description: RISC-V IOMMU as a PCI device connected to root port
> > +        items:
> > +          - enum:
> > +              - vendor,chip-pci-iommu
> > +          - const: riscv,pci-iommu
> > +
> > +  reg:
> > +    maxItems: 1
> > +    description:
> > +      For RISC-V IOMMU as a platform device, this represents the MMIO base
> > +      address of registers.
> > +
> > +      For RISC-V IOMMU as a PCI device, this represents the PCI-PCI bridge
> > +      details as described in Documentation/devicetree/bindings/pci/pci.txt
> > +
> > +  '#iommu-cells':
> > +    const: 2
> > +    description: |
> > +      Each IOMMU specifier represents the base device ID and number of
> > +      device IDs.
> > +
> > +  interrupts:
> > +    minItems: 1
> > +    maxItems: 16
> > +    description:
> > +      The presence of this property implies that given RISC-V IOMMU uses
> > +      wired interrupts to notify the RISC-V HARTS (or CPUs).
> > +
> > +  msi-parent:
> > +    description:
> > +      The presence of this property implies that given RISC-V IOMMU uses
> > +      MSIx to notify the RISC-V HARTs (or CPUs). This property should be
> > +      considered only when the interrupts property is absent.
> > +
> > +  dma-coherent:
> > +    description:
> > +      Present if page table walks and DMA accessed made by the RISC-V IOMMU
> > +      are cache coherent with the CPU.
> > +
> > +  power-domains:
> > +    maxItems: 1
> > +
>
> In RISC-V IOMMU, certain devices can be set to bypass mode when the
> IOMMU is in translation mode. To identify the devices that require
> bypass mode by default, does it be sensible to add a property to
> indicate this behavior?

Bypass mode for a device is a property of that device (similar to dma-coherent)
and not of the IOMMU. Other architectures (ARM and x86) never added such
a device property for bypass mode so I guess it is NOT ADVISABLE to do it.

If this is REALLY required then we can do something similar to the QCOM
SMMU driver where they have a whitelist of devices which are allowed to
be in bypass mode (i.e. IOMMU_DOMAIN_IDENTITY) based their device
compatible string and any device outside this whitelist is blocked by default.

Regards,
Anup

>
> > +required:
> > +  - compatible
> > +  - reg
> > +  - '#iommu-cells'
> > +
> > +additionalProperties: false
> > +
> > +examples:
> > +  - |
> > +    /* Example 1 (IOMMU platform device with wired interrupts) */
> > +    immu1: iommu@1bccd000 {
> > +        compatible = "vendor,chip-iommu", "riscv,iommu";
> > +        reg = <0x1bccd000 0x1000>;
> > +        interrupt-parent = <&aplic_smode>;
> > +        interrupts = <32 4>, <33 4>, <34 4>, <35 4>;
> > +        #iommu-cells = <2>;
> > +    };
> > +
> > +    /* Device with two IOMMU device IDs, 0 and 7 */
> > +    master1 {
> > +        iommus = <&immu1 0 1>, <&immu1 7 1>;
> > +    };
> > +
> > +  - |
> > +    /* Example 2 (IOMMU platform device with MSIs) */
> > +    immu2: iommu@1bcdd000 {
> > +        compatible = "vendor,chip-iommu", "riscv,iommu";
> > +        reg = <0x1bccd000 0x1000>;
> > +        msi-parent = <&imsics_smode>;
> > +        #iommu-cells = <2>;
> > +    };
> > +
> > +    bus {
> > +        #address-cells = <2>;
> > +        #size-cells = <2>;
> > +
> > +        /* Device with IOMMU device IDs ranging from 32 to 64 */
> > +        master1 {
> > +                iommus = <&immu2 32 32>;
> > +        };
> > +
> > +        pcie@40000000 {
> > +            compatible = "pci-host-cam-generic";
> > +            device_type = "pci";
> > +            #address-cells = <3>;
> > +            #size-cells = <2>;
> > +            bus-range = <0x0 0x1>;
> > +
> > +            /* CPU_PHYSICAL(2)  SIZE(2) */
> > +            reg = <0x0 0x40000000 0x0 0x1000000>;
> > +
> > +            /* BUS_ADDRESS(3)  CPU_PHYSICAL(2)  SIZE(2) */
> > +            ranges = <0x01000000 0x0 0x01000000  0x0 0x01000000  0x0 0x00010000>,
> > +                     <0x02000000 0x0 0x41000000  0x0 0x41000000  0x0 0x3f000000>;
> > +
> > +            #interrupt-cells = <0x1>;
> > +
> > +            /* PCI_DEVICE(3)  INT#(1)  CONTROLLER(PHANDLE)  CONTROLLER_DATA(2) */
> > +            interrupt-map = <   0x0 0x0 0x0  0x1  &aplic_smode  0x4 0x1>,
> > +                            < 0x800 0x0 0x0  0x1  &aplic_smode  0x5 0x1>,
> > +                            <0x1000 0x0 0x0  0x1  &aplic_smode  0x6 0x1>,
> > +                            <0x1800 0x0 0x0  0x1  &aplic_smode  0x7 0x1>;
> > +
> > +            /* PCI_DEVICE(3)  INT#(1) */
> > +            interrupt-map-mask = <0xf800 0x0 0x0  0x7>;
> > +
> > +            msi-parent = <&imsics_smode>;
> > +
> > +            /* Devices with bus number 0-127 are mastered via immu2 */
> > +            iommu-map = <0x0000 &immu2 0x0000 0x8000>;
> > +        };
> > +    };
> > +...
> > --
> > 2.34.1
> >
> >
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