Re: [RFC PATCH 11/36] dt-bindings: arm: Add MPAM MSC binding

[Rob Herring <robh@kernel.org>]

On Fri, Jul 11, 2025 at 06:36:23PM +0000, James Morse wrote:
> From: Rob Herring <robh@kernel.org>
> 
> The binding is designed around the assumption that an MSC will be a
> sub-block of something else such as a memory controller, cache controller,
> or IOMMU. However, it's certainly possible a design does not have that
> association or has a mixture of both, so the binding illustrates how we can
> support that with RIS child nodes.
> 
> A key part of MPAM is we need to know about all of the MSCs in the system
> before it can be enabled. This drives the need for the genericish
> 'arm,mpam-msc' compatible. Though we can't assume an MSC is accessible
> until a h/w specific driver potentially enables the h/w.
> 
> Cc: James Morse <james.morse@arm.com>
> Signed-off-by: Rob Herring <robh@kernel.org>
> Signed-off-by: James Morse <james.morse@arm.com>
> ---
>  .../devicetree/bindings/arm/arm,mpam-msc.yaml | 227 ++++++++++++++++++
>  1 file changed, 227 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/arm/arm,mpam-msc.yaml

Is there any DT based h/w using this? I'm not aware of any. I would 
prefer not merging this until there is. I have little insight whether 
these genericish compatibles will be sufficient, but I have lots of 
experience to say they won't be. I would also suspect that if anyone has 
started using this, they've just extended/modified it however they 
wanted and no feedback got to me.


> diff --git a/Documentation/devicetree/bindings/arm/arm,mpam-msc.yaml b/Documentation/devicetree/bindings/arm/arm,mpam-msc.yaml
> new file mode 100644
> index 000000000000..9d542ecb1a7d
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/arm/arm,mpam-msc.yaml
> @@ -0,0 +1,227 @@
> +# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/arm/arm,mpam-msc.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: Arm Memory System Resource Partitioning and Monitoring (MPAM)
> +
> +description: |
> +  The Arm MPAM specification can be found here:
> +
> +  https://developer.arm.com/documentation/ddi0598/latest
> +
> +maintainers:
> +  - Rob Herring <robh@kernel.org>
> +
> +properties:
> +  compatible:
> +    items:
> +      - const: arm,mpam-msc                   # Further details are discoverable
> +      - const: arm,mpam-memory-controller-msc
> +
> +  reg:
> +    maxItems: 1
> +    description: A memory region containing registers as defined in the MPAM
> +      specification.
> +
> +  interrupts:
> +    minItems: 1
> +    items:
> +      - description: error (optional)
> +      - description: overflow (optional, only for monitoring)
> +
> +  interrupt-names:
> +    oneOf:
> +      - items:
> +          - enum: [ error, overflow ]
> +      - items:
> +          - const: error
> +          - const: overflow
> +
> +  arm,not-ready-us:
> +    description: The maximum time in microseconds for monitoring data to be
> +      accurate after a settings change. For more information, see the
> +      Not-Ready (NRDY) bit description in the MPAM specification.
> +
> +  numa-node-id: true # see NUMA binding
> +
> +  '#address-cells':
> +    const: 1
> +
> +  '#size-cells':
> +    const: 0
> +
> +patternProperties:
> +  '^ris@[0-9a-f]$':
> +    type: object
> +    additionalProperties: false
> +    description: |

'|' can be dropped.

> +      RIS nodes for each RIS in an MSC. These nodes are required for each RIS
> +      implementing known MPAM controls
> +
> +    properties:
> +      compatible:
> +        enum:
> +            # Bulk storage for cache
> +          - arm,mpam-cache
> +            # Memory bandwidth
> +          - arm,mpam-memory
> +
> +      reg:
> +        minimum: 0
> +        maximum: 0xf
> +
> +      cpus:
> +        $ref: '/schemas/types.yaml#/definitions/phandle-array'

Don't need the type. It's in the core schemas now.

> +        description:
> +          Phandle(s) to the CPU node(s) this RIS belongs to. By default, the parent
> +          device's affinity is used.
> +
> +      arm,mpam-device:
> +        $ref: '/schemas/types.yaml#/definitions/phandle'

Don't need quotes. This should be a warning, but no testing happened 
because the DT list and maintainers weren't CCed.

> +        description:
> +          By default, the MPAM enabled device associated with a RIS is the MSC's
> +          parent node. It is possible for each RIS to be associated with different
> +          devices in which case 'arm,mpam-device' should be used.
> +
> +    required:
> +      - compatible
> +      - reg
> +
> +required:
> +  - compatible
> +  - reg
> +
> +dependencies:
> +  interrupts: [ interrupt-names ]
> +
> +additionalProperties: false
> +
> +examples:
> +  - |
> +    /*
> +    cpus {
> +        cpu@0 {
> +            next-level-cache = <&L2_0>;
> +        };
> +        cpu@100 {
> +            next-level-cache = <&L2_1>;
> +        };
> +    };
> +    */
> +    L2_0: cache-controller-0 {
> +        compatible = "cache";
> +        cache-level = <2>;
> +        cache-unified;
> +        next-level-cache = <&L3>;
> +
> +    };
> +
> +    L2_1: cache-controller-1 {
> +        compatible = "cache";
> +        cache-level = <2>;
> +        cache-unified;
> +        next-level-cache = <&L3>;
> +
> +    };

All the above should be dropped. Not part of this binding.

> +
> +    L3: cache-controller@30000000 {
> +        compatible = "arm,dsu-l3-cache", "cache";

Pretty sure this is a warning because that compatible doesn't exist.

> +        cache-level = <3>;
> +        cache-unified;
> +
> +        ranges = <0x0 0x30000000 0x800000>;
> +        #address-cells = <1>;
> +        #size-cells = <1>;
> +
> +        msc@10000 {
> +            compatible = "arm,mpam-msc";
> +
> +            /* CPU affinity implied by parent cache node's  */
> +            reg = <0x10000 0x2000>;
> +            interrupts = <1>, <2>;
> +            interrupt-names = "error", "overflow";
> +            arm,not-ready-us = <1>;
> +        };
> +    };
> +
> +    mem: memory-controller@20000 {
> +        compatible = "foo,a-memory-controller";
> +        reg = <0x20000 0x1000>;
> +
> +        #address-cells = <1>;
> +        #size-cells = <1>;
> +        ranges;
> +
> +        msc@21000 {
> +            compatible = "arm,mpam-memory-controller-msc", "arm,mpam-msc";
> +            reg = <0x21000 0x1000>;
> +            interrupts = <3>;
> +            interrupt-names = "error";
> +            arm,not-ready-us = <1>;
> +            numa-node-id = <1>;
> +        };
> +    };
> +
> +    iommu@40000 {
> +        reg = <0x40000 0x1000>;
> +
> +        ranges;
> +        #address-cells = <1>;
> +        #size-cells = <1>;
> +
> +        msc@41000 {
> +            compatible = "arm,mpam-msc";
> +            reg = <0 0x1000>;
> +            interrupts = <5>, <6>;
> +            interrupt-names = "error", "overflow";
> +            arm,not-ready-us = <1>;
> +
> +            #address-cells = <1>;
> +            #size-cells = <0>;
> +
> +            ris@2 {
> +                compatible = "arm,mpam-cache";
> +                reg = <0>;
> +                // TODO: How to map to device(s)?
> +            };
> +        };
> +    };
> +
> +    msc@80000 {
> +        compatible = "foo,a-standalone-msc";
> +        reg = <0x80000 0x1000>;
> +
> +        clocks = <&clks 123>;
> +
> +        ranges;
> +        #address-cells = <1>;
> +        #size-cells = <1>;
> +
> +        msc@10000 {
> +            compatible = "arm,mpam-msc";
> +
> +            reg = <0x10000 0x2000>;
> +            interrupts = <7>;
> +            interrupt-names = "overflow";
> +            arm,not-ready-us = <1>;
> +
> +            #address-cells = <1>;
> +            #size-cells = <0>;
> +
> +            ris@0 {
> +                compatible = "arm,mpam-cache";
> +                reg = <0>;
> +                arm,mpam-device = <&L2_0>;
> +            };
> +
> +            ris@1 {
> +                compatible = "arm,mpam-memory";
> +                reg = <1>;
> +                arm,mpam-device = <&mem>;
> +            };
> +        };
> +    };
> +
> +...
> -- 
> 2.39.5
>