Re: [PATCH 4/9] dt-bindings: Add RISC-V incoming MSI controller bindings

[Conor Dooley <conor@kernel.org>]

Hey Anup,

On Fri, Nov 11, 2022 at 10:12:02AM +0530, Anup Patel wrote:
> dt-bindings: Add RISC-V incoming MSI controller bindings

nit: it looks like the usual prefix here is "dt-bindings:
interrupt-controller".

> We add DT bindings document for RISC-V incoming MSI controller (IMSIC)
> defined by the RISC-V advanced interrupt architecture (AIA) specification.
> 
> Signed-off-by: Anup Patel <apatel@ventanamicro.com>
> ---
>  .../interrupt-controller/riscv,imsic.yaml     | 174 ++++++++++++++++++
>  1 file changed, 174 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/interrupt-controller/riscv,imsic.yaml
> 
> diff --git a/Documentation/devicetree/bindings/interrupt-controller/riscv,imsic.yaml b/Documentation/devicetree/bindings/interrupt-controller/riscv,imsic.yaml
> new file mode 100644
> index 000000000000..05106eb1955e
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/interrupt-controller/riscv,imsic.yaml
> @@ -0,0 +1,174 @@
> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/interrupt-controller/riscv,imsic.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: RISC-V Incoming MSI Controller (IMSIC)
> +
> +maintainers:
> +  - Anup Patel <anup@brainfault.org>
> +
> +description:

Is this one of the situations where we want to have a | after
"description:" to preserve formatting?

> +  The RISC-V advanced interrupt architecture (AIA) defines a per-CPU incoming
> +  MSI controller (IMSIC) for handling MSIs in a RISC-V platform. The RISC-V
> +  AIA specification can be found at https://github.com/riscv/riscv-aia.
> +
> +  The IMSIC is a per-CPU (or per-HART) device with separate interrupt file
> +  for each privilege level (machine or supervisor). The configuration of
> +  a IMSIC interrupt file is done using AIA CSRs and it also has a 4KB MMIO
> +  space to receive MSIs from devices. Each IMSIC interrupt file supports a
> +  fixed number of interrupt identities (to distinguish MSIs from devices)
> +  which is same for given privilege level across CPUs (or HARTs).
> +
> +  The arrangement of IMSIC interrupt files in MMIO space of a RISC-V platform
> +  follows a particular scheme defined by the RISC-V AIA specification. A IMSIC
> +  group is a set of IMSIC interrupt files co-located in MMIO space and we can
> +  have multiple IMSIC groups (i.e. clusters, sockets, chiplets, etc) in a
> +  RISC-V platform. The MSI target address of a IMSIC interrupt file at given
> +  privilege level (machine or supervisor) encodes group index, HART index,
> +  and guest index (shown below).
> +
> +  XLEN-1           >=24                                 12    0
> +  |                  |                                  |     |
> +  -------------------------------------------------------------
> +  |xxxxxx|Group Index|xxxxxxxxxxx|HART Index|Guest Index|  0  |
> +  -------------------------------------------------------------
> +
> +  The device tree of a RISC-V platform will have one IMSIC device tree node
> +  for each privilege level (machine or supervisor) which collectively describe
> +  IMSIC interrupt files at that privilege level across CPUs (or HARTs).
> +
> +allOf:
> +  - $ref: /schemas/interrupt-controller.yaml#
> +
> +properties:
> +  compatible:
> +    items:
> +      - enum:
> +          - vendor,chip-imsics

Is it valid to have a dummy here? I did a bit of grepping & could not
see a single other yaml binding which used a placeholder like this -
other than the example schema itself. I assume you're trying to get
across the point that using the bare riscv,imsics is not okay and a
vendor should create a custom string for their implementation?

Also, the file name says "riscv,imsic", the description says "IMSIC" but
you've used "imsics" in the compatible. Is this a typo, or a plural?

Thanks,
Conor.

> +      - const: riscv,imsics
> +
> +  reg:
> +    minItems: 1
> +    maxItems: 128
> +    description:
> +      Base address of each IMSIC group.
> +
> +  interrupt-controller: true
> +
> +  "#interrupt-cells":
> +    const: 0
> +
> +  msi-controller: true
> +
> +  interrupts-extended:
> +    minItems: 1
> +    maxItems: 32768
> +    description:
> +      This property represents the set of CPUs (or HARTs) for which given
> +      device tree node describes the IMSIC interrupt files. Each node pointed
> +      to should be a riscv,cpu-intc node, which has a riscv node (i.e. RISC-V
> +      HART) as parent.
> +
> +  riscv,num-ids:
> +    $ref: /schemas/types.yaml#/definitions/uint32
> +    minimum: 63
> +    maximum: 2047
> +    description:
> +      Specifies how many interrupt identities are supported by IMSIC interrupt
> +      file.
> +
> +  riscv,num-guest-ids:
> +    $ref: /schemas/types.yaml#/definitions/uint32
> +    minimum: 63
> +    maximum: 2047
> +    description:
> +      Specifies how many interrupt identities are supported by IMSIC guest
> +      interrupt file. When not specified the number of interrupt identities
> +      supported by IMSIC guest file is assumed to be same as specified by
> +      the riscv,num-ids property.
> +
> +  riscv,slow-ipi:
> +    type: boolean
> +    description:
> +      The presence of this property implies that software interrupts (i.e.
> +      IPIs) using IMSIC software injected MSIs is slower compared to other
> +      software interrupt mechanisms (such as SBI IPI) on the underlying
> +      RISC-V platform.
> +
> +  riscv,guest-index-bits:
> +    minimum: 0
> +    maximum: 7
> +    description:
> +      Specifies number of guest index bits in the MSI target address. When
> +      not specified it is assumed to be 0.
> +
> +  riscv,hart-index-bits:
> +    minimum: 0
> +    maximum: 15
> +    description:
> +      Specifies number of HART index bits in the MSI target address. When
> +      not specified it is estimated based on the interrupts-extended property.
> +
> +  riscv,group-index-bits:
> +    minimum: 0
> +    maximum: 7
> +    description:
> +      Specifies number of group index bits in the MSI target address. When
> +      not specified it is assumed to be 0.
> +
> +  riscv,group-index-shift:
> +    $ref: /schemas/types.yaml#/definitions/uint32
> +    minimum: 24
> +    maximum: 55
> +    description:
> +      Specifies the least significant bit of the group index bits in the
> +      MSI target address. When not specified it is assumed to be 24.
> +
> +additionalProperties: false
> +
> +required:
> +  - compatible
> +  - reg
> +  - interrupt-controller
> +  - msi-controller
> +  - interrupts-extended
> +  - riscv,num-ids
> +
> +examples:
> +  - |
> +    // Example 1 (Machine-level IMSIC files with just one group):
> +
> +    imsic_mlevel: interrupt-controller@24000000 {
> +      compatible = "vendor,chip-imsics", "riscv,imsics";
> +      interrupts-extended = <&cpu1_intc 11>,
> +                            <&cpu2_intc 11>,
> +                            <&cpu3_intc 11>,
> +                            <&cpu4_intc 11>;
> +      reg = <0x28000000 0x4000>;
> +      interrupt-controller;
> +      #interrupt-cells = <0>;
> +      msi-controller;
> +      riscv,num-ids = <127>;
> +    };
> +
> +  - |
> +    // Example 2 (Supervisor-level IMSIC files with two groups):
> +
> +    imsic_slevel: interrupt-controller@28000000 {
> +      compatible = "vendor,chip-imsics", "riscv,imsics";
> +      interrupts-extended = <&cpu1_intc 9>,
> +                            <&cpu2_intc 9>,
> +                            <&cpu3_intc 9>,
> +                            <&cpu4_intc 9>;
> +      reg = <0x28000000 0x2000>, /* Group0 IMSICs */
> +            <0x29000000 0x2000>; /* Group1 IMSICs */
> +      interrupt-controller;
> +      #interrupt-cells = <0>;
> +      msi-controller;
> +      riscv,num-ids = <127>;
> +      riscv,group-index-bits = <1>;
> +      riscv,group-index-shift = <24>;
> +    };
> +...
> -- 
> 2.34.1
> 
> 
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