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

Conor Dooley
2022-11-13T14:48:48Z

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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