Re: [PATCH v10 07/15] dt-bindings: interrupt-controller: Add RISC-V incoming MSI controller

[Anup Patel <apatel@ventanamicro.com>]

On Thu, Oct 12, 2023 at 10:05 PM Conor Dooley <conor@kernel.org> wrote:
>
> Hey,
>
> On Tue, Oct 03, 2023 at 10:13:55AM +0530, Anup Patel wrote:
> > We add DT bindings document for the RISC-V incoming MSI controller
> > (IMSIC) defined by the RISC-V advanced interrupt architecture (AIA)
> > specification.
> >
> > Signed-off-by: Anup Patel <apatel@ventanamicro.com>
> > Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
>
> Just FYI, since they'll reply to this themselves, but some of the
> Microchip folks have run into problems with sparse hart indexes while
> trying to use the imsic binding to describe some configurations they
> have. I think there were also so problems with how to describe to a
> linux guest which file to use, when the first hart available to the
> guest does not use the first file. They'll do a better job of describing
> their problems than I will, so I shall leave it to them!

Quoting AIA spec:
"For the purpose of locating the memory pages of interrupt files in the
address space, assume each hart (or each hart within a group) has a
unique hart number that may or may not be related to the unique hart
identifiers (“hart IDs”) that the RISC-V Privileged Architecture assigns
to harts."

It is very easy to get confused between the AIA "hart index" and
"hart IDs" defined by the RISC-V Privileged specification but these
are two very different things. The AIA "hart index" over here is the
bits in the address of an IMSIC file.

This DT binding follows the IMSIC file arrangement in the address
space as defined by the section "3.6 Arrangement of the memory
regions of multiple interrupt files" of the AIA specification. This
arrangement is MANDATORY for platforms having both APLIC
and IMSIC because in MSI-mode the APLIC generates target
MSI address based the IMSIC file arrangement described in the
section "3.6 Arrangement of the memory regions of multiple
interrupt files". In fact, this also applies to virtual platforms
created by hypervisors (KVM, Xen, ...)

Regards,
Anup


>
> Cheers,
> Conor.
>
> > Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
> > ---
> >  .../interrupt-controller/riscv,imsics.yaml    | 172 ++++++++++++++++++
> >  1 file changed, 172 insertions(+)
> >  create mode 100644 Documentation/devicetree/bindings/interrupt-controller/riscv,imsics.yaml
> >
> > diff --git a/Documentation/devicetree/bindings/interrupt-controller/riscv,imsics.yaml b/Documentation/devicetree/bindings/interrupt-controller/riscv,imsics.yaml
> > new file mode 100644
> > index 000000000000..84976f17a4a1
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/interrupt-controller/riscv,imsics.yaml
> > @@ -0,0 +1,172 @@
> > +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> > +%YAML 1.2
> > +---
> > +$id: http://devicetree.org/schemas/interrupt-controller/riscv,imsics.yaml#
> > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > +
> > +title: RISC-V Incoming MSI Controller (IMSIC)
> > +
> > +maintainers:
> > +  - Anup Patel <anup@brainfault.org>
> > +
> > +description: |
> > +  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 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).
> > +
> > +  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            > (HART Index MSB)                  12    0
> > +  |                  |                                  |     |
> > +  -------------------------------------------------------------
> > +  |xxxxxx|Group Index|xxxxxxxxxxx|HART Index|Guest Index|  0  |
> > +  -------------------------------------------------------------
> > +
> > +allOf:
> > +  - $ref: /schemas/interrupt-controller.yaml#
> > +  - $ref: /schemas/interrupt-controller/msi-controller.yaml#
> > +
> > +properties:
> > +  compatible:
> > +    items:
> > +      - enum:
> > +          - qemu,imsics
> > +      - const: riscv,imsics
> > +
> > +  reg:
> > +    minItems: 1
> > +    maxItems: 16384
> > +    description:
> > +      Base address of each IMSIC group.
> > +
> > +  interrupt-controller: true
> > +
> > +  "#interrupt-cells":
> > +    const: 0
> > +
> > +  msi-controller: true
> > +
> > +  "#msi-cells":
> > +    const: 0
> > +
> > +  interrupts-extended:
> > +    minItems: 1
> > +    maxItems: 16384
> > +    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 CPU node (i.e. RISC-V
> > +      HART) as parent.
> > +
> > +  riscv,num-ids:
> > +    $ref: /schemas/types.yaml#/definitions/uint32
> > +    minimum: 63
> > +    maximum: 2047
> > +    description:
> > +      Number of interrupt identities supported by IMSIC interrupt file.
> > +
> > +  riscv,num-guest-ids:
> > +    $ref: /schemas/types.yaml#/definitions/uint32
> > +    minimum: 63
> > +    maximum: 2047
> > +    description:
> > +      Number of interrupt identities are supported by IMSIC guest interrupt
> > +      file. When not specified it is assumed to be same as specified by the
> > +      riscv,num-ids property.
> > +
> > +  riscv,guest-index-bits:
> > +    minimum: 0
> > +    maximum: 7
> > +    default: 0
> > +    description:
> > +      Number of guest index bits in the MSI target address.
> > +
> > +  riscv,hart-index-bits:
> > +    minimum: 0
> > +    maximum: 15
> > +    description:
> > +      Number of HART index bits in the MSI target address. When not
> > +      specified it is calculated based on the interrupts-extended property.
> > +
> > +  riscv,group-index-bits:
> > +    minimum: 0
> > +    maximum: 7
> > +    default: 0
> > +    description:
> > +      Number of group index bits in the MSI target address.
> > +
> > +  riscv,group-index-shift:
> > +    $ref: /schemas/types.yaml#/definitions/uint32
> > +    minimum: 0
> > +    maximum: 55
> > +    default: 24
> > +    description:
> > +      The least significant bit position of the group index bits in the
> > +      MSI target address.
> > +
> > +required:
> > +  - compatible
> > +  - reg
> > +  - interrupt-controller
> > +  - msi-controller
> > +  - "#msi-cells"
> > +  - interrupts-extended
> > +  - riscv,num-ids
> > +
> > +unevaluatedProperties: false
> > +
> > +examples:
> > +  - |
> > +    // Example 1 (Machine-level IMSIC files with just one group):
> > +
> > +    interrupt-controller@24000000 {
> > +      compatible = "qemu,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;
> > +      #msi-cells = <0>;
> > +      riscv,num-ids = <127>;
> > +    };
> > +
> > +  - |
> > +    // Example 2 (Supervisor-level IMSIC files with two groups):
> > +
> > +    interrupt-controller@28000000 {
> > +      compatible = "qemu,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;
> > +      #msi-cells = <0>;
> > +      riscv,num-ids = <127>;
> > +      riscv,group-index-bits = <1>;
> > +      riscv,group-index-shift = <24>;
> > +    };
> > +...
> > --
> > 2.34.1
> >

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