Re: [PATCH 6/9] dt-bindings: Add RISC-V advanced PLIC bindings

[Anup Patel <anup@brainfault.org>]

On Thu, Nov 17, 2022 at 12:57 AM Rob Herring <robh@kernel.org> wrote:
>
> On Fri, Nov 11, 2022 at 10:12:04AM +0530, Anup Patel wrote:
> > We add DT bindings document for RISC-V advanced platform level interrupt
> > controller (APLIC) defined by the RISC-V advanced interrupt architecture
> > (AIA) specification.
> >
> > Signed-off-by: Anup Patel <apatel@ventanamicro.com>
> > ---
> >  .../interrupt-controller/riscv,aplic.yaml     | 136 ++++++++++++++++++
> >  1 file changed, 136 insertions(+)
> >  create mode 100644 Documentation/devicetree/bindings/interrupt-controller/riscv,aplic.yaml
> >
> > diff --git a/Documentation/devicetree/bindings/interrupt-controller/riscv,aplic.yaml b/Documentation/devicetree/bindings/interrupt-controller/riscv,aplic.yaml
> > new file mode 100644
> > index 000000000000..0aa48571f3bc
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/interrupt-controller/riscv,aplic.yaml
> > @@ -0,0 +1,136 @@
> > +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> > +%YAML 1.2
> > +---
> > +$id: http://devicetree.org/schemas/interrupt-controller/riscv,aplic.yaml#
> > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > +
> > +title: RISC-V Advancded Platform Level Interrupt Controller (APLIC)
> > +
> > +maintainers:
> > +  - Anup Patel <anup@brainfault.org>
> > +
> > +description:
> > +  The RISC-V advanced interrupt architecture (AIA) defines advanced platform
> > +  level interrupt controller (APLIC) for handling wired interrupts in a
> > +  RISC-V platform. The RISC-V AIA specification can be found at
> > +  https://github.com/riscv/riscv-aia.
> > +
> > +  The RISC-V APLIC is implemented as hierarchical APLIC domains where all
> > +  interrupt sources connect to the root domain which can further delegate
> > +  interrupts to child domains. We have one device tree node for each APLIC
> > +  domain.
> > +
> > +allOf:
> > +  - $ref: /schemas/interrupt-controller.yaml#
> > +
> > +properties:
> > +  compatible:
> > +    items:
> > +      - enum:
> > +          - vendor,chip-aplic
> > +      - const: riscv,aplic
> > +
> > +  reg:
> > +    maxItems: 1
> > +
> > +  interrupt-controller: true
> > +
> > +  "#interrupt-cells":
> > +    const: 2
> > +
> > +  interrupts-extended:
> > +    minItems: 1
> > +    maxItems: 16384
> > +    description:
> > +      The presence of this property implies that given APLIC domain directly
> > +      injects external interrupts to a set of RISC-V HARTS (or CPUs). Each
> > +      node pointed to should be a riscv,cpu-intc node, which has a riscv node
> > +      (i.e. RISC-V HART) as parent.
> > +
> > +  msi-parent:
> > +    description:
> > +      The presence of this property implies that given APLIC domain forwards
> > +      wired interrupts as MSIs to a AIA incoming message signaled interrupt
> > +      controller (IMSIC). This property should be considered only when the
> > +      interrupts-extended property is absent.
> > +
> > +  riscv,num-sources:
> > +    $ref: "/schemas/types.yaml#/definitions/uint32"
> > +    minimum: 1
> > +    maximum: 1023
> > +    description:
> > +      Specifies how many wired interrupts are supported by this APLIC domain.
> > +
> > +  riscv,children:
> > +    $ref: '/schemas/types.yaml#/definitions/phandle-array'
> > +    minItems: 1
> > +    maxItems: 1024
>
> As each entry is a single phandle:
>
>        items:
>          maxItems: 1

Okay, I will update.

>
> > +    description:
> > +      This property represents a list of child APLIC domains for the given
> > +      APLIC domain. Each child APLIC domain is assigned child index in
> > +      increasing order with the first child APLIC domain assigned child
> > +      index 0. The APLIC domain child index is used by firmware to delegate
> > +      interrupts from the given APLIC domain to a particular child APLIC
> > +      domain.
> > +
> > +  riscv,delegate:
> > +    $ref: '/schemas/types.yaml#/definitions/phandle-array'
> > +    minItems: 1
> > +    maxItems: 1024
>
>        items:
>          items:
>            - description: child APLIC domain phandle
>            - description: ...
>            - description: ...

Okay, I will update.

>
> > +    description:
> > +      This property represents a interrupt delegation list where each entry
> > +      is a triple consisting of child APLIC domain phandle, first interrupt
> > +      number, and last interrupt number. The firmware will configure interrupt
> > +      delegation registers based on interrupt delegation list.
>
> First and last are inclusive?

Yes, first and last are inclusive. I will clarify this in the description.

>
> Couldn't riscv,children and riscv,delegate be combined? How would they
> be different? If some children don't have any delegated interrupts, you
> could use -1 for the cells for example.

The "riscv,children" describes the hierarchy of APLIC domains in HW
whereas "riscv,delegate" describes the system choices of delegating
interrupts from a parent APLIC domain to one of its children. I feel
it's not natural to combine these two properties.

>
> An example showing the need would be nice.
>
> > +
> > +additionalProperties: false
> > +
> > +required:
> > +  - compatible
> > +  - reg
> > +  - interrupt-controller
> > +  - "#interrupt-cells"
> > +  - riscv,num-sources
> > +
> > +examples:
> > +  - |
> > +    // Example 1 (APIC domain directly injecting interrupt to HARTs):
>
> Is than an x86 APIC or a typo?
>
> > +
> > +    aplic0: interrupt-controller@c000000 {
> > +      compatible = "vendor,chip-aplic", "riscv,aplic";
> > +      interrupts-extended = <&cpu1_intc 11>,
> > +                            <&cpu2_intc 11>,
> > +                            <&cpu3_intc 11>,
> > +                            <&cpu4_intc 11>;
> > +      reg = <0xc000000 0x4080>;
> > +      interrupt-controller;
> > +      #interrupt-cells = <2>;
> > +      riscv,num-sources = <63>;
> > +      riscv,children = <&aplic1>;
> > +      riscv,delegate = <&aplic1 1 63>;
> > +    };
> > +
> > +    aplic1: interrupt-controller@d000000 {
> > +      compatible = "vendor,chip-aplic", "riscv,aplic";
> > +      interrupts-extended = <&cpu1_intc 9>,
> > +                            <&cpu2_intc 9>,
> > +                            <&cpu3_intc 9>,
> > +                            <&cpu4_intc 9>;
> > +      reg = <0xd000000 0x4080>;
> > +      interrupt-controller;
> > +      #interrupt-cells = <2>;
> > +      riscv,num-sources = <63>;
> > +    };
> > +
> > +  - |
> > +    // Example 2 (APIC domain forwarding interrupts as MSIs):
> > +
> > +    interrupt-controller@d000000 {
> > +      compatible = "vendor,chip-aplic", "riscv,aplic";
> > +      msi-parent = <&imsics>;
> > +      reg = <0xd000000 0x4000>;
> > +      interrupt-controller;
> > +      #interrupt-cells = <2>;
> > +      riscv,num-sources = <63>;
> > +    };
> > +...
> > --
> > 2.34.1
> >
> >

Regards,
Anup