linux/Documentation/devicetree/bindings/reserved-memory/reserved-memory.yaml

# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
%YAML 1.2
---
$id: http://devicetree.org/schemas/reserved-memory/reserved-memory.yaml#
$schema: http://devicetree.org/meta-schemas/core.yaml#

title: /reserved-memory Child Node Common

maintainers:
  - devicetree-spec@vger.kernel.org

description: >
  Reserved memory is specified as a node under the /reserved-memory node. The
  operating system shall exclude reserved memory from normal usage one can
  create child nodes describing particular reserved (excluded from normal use)
  memory regions. Such memory regions are usually designed for the special
  usage by various device drivers.

  Each child of the reserved-memory node specifies one or more regions
  of reserved memory. Each child node may either use a 'reg' property to
  specify a specific range of reserved memory, or a 'size' property with
  optional constraints to request a dynamically allocated block of
  memory.

  Following the generic-names recommended practice, node names should
  reflect the purpose of the node (ie. "framebuffer" or "dma-pool").
  Unit address (@<address>) should be appended to the name if the node
  is a static allocation.

properties:
  reg: true

  size:
    oneOf:
      - $ref: /schemas/types.yaml#/definitions/uint32
      - $ref: /schemas/types.yaml#/definitions/uint64
    description: >
      Length based on parent's \#size-cells. Size in bytes of memory to
      reserve.

  alignment:
    oneOf:
      - $ref: /schemas/types.yaml#/definitions/uint32
      - $ref: /schemas/types.yaml#/definitions/uint64
    description: >
      Length based on parent's \#size-cells. Address boundary for
      alignment of allocation.

  alloc-ranges:
    $ref: /schemas/types.yaml#/definitions/uint32-array
    description: >
      Address and Length pairs. Specifies regions of memory that are
      acceptable to allocate from.

  iommu-addresses:
    $ref: /schemas/types.yaml#/definitions/phandle-array
    description: >
      A list of phandle and specifier pairs that describe static IO virtual
      address space mappings and carveouts associated with a given reserved
      memory region. The phandle in the first cell refers to the device for
      which the mapping or carveout is to be created.

      The specifier consists of an address/size pair and denotes the IO
      virtual address range of the region for the given device. The exact
      format depends on the values of the "#address-cells" and "#size-cells"
      properties of the device referenced via the phandle.

      When used in combination with a "reg" property, an IOVA mapping is to
      be established for this memory region. One example where this can be
      useful is to create an identity mapping for physical memory that the
      firmware has configured some hardware to access (such as a bootsplash
      framebuffer).

      If no "reg" property is specified, the "iommu-addresses" property
      defines carveout regions in the IOVA space for the given device. This
      can be useful if a certain memory region should not be mapped through
      the IOMMU.

  no-map:
    type: boolean
    description: >
      Indicates the operating system must not create a virtual mapping
      of the region as part of its standard mapping of system memory,
      nor permit speculative access to it under any circumstances other
      than under the control of the device driver using the region.

  reusable:
    type: boolean
    description: >
      The operating system can use the memory in this region with the
      limitation that the device driver(s) owning the region need to be
      able to reclaim it back. Typically that means that the operating
      system can use that region to store volatile or cached data that
      can be otherwise regenerated or migrated elsewhere.

allOf:
  - if:
      required:
        - no-map

    then:
      not:
        required:
          - reusable

  - if:
      required:
        - reusable

    then:
      not:
        required:
          - no-map

oneOf:
  - oneOf:
      - required:
          - reg

      - required:
          - size

  - oneOf:
      # IOMMU reservations
      - required:
          - iommu-addresses

      # IOMMU mappings
      - required:
          - reg
          - iommu-addresses

additionalProperties: true

examples:
  - |
    / {
      compatible = "foo";
      model = "foo";

      #address-cells = <2>;
      #size-cells = <2>;

      reserved-memory {
        #address-cells = <2>;
        #size-cells = <2>;
        ranges;

        adsp_resv: reservation-adsp {
          /*
           * Restrict IOVA mappings for ADSP buffers to the 512 MiB region
           * from 0x40000000 - 0x5fffffff. Anything outside is reserved by
           * the ADSP for I/O memory and private memory allocations.
           */
          iommu-addresses = <&adsp 0x0 0x00000000 0x00 0x40000000>,
                            <&adsp 0x0 0x60000000 0xff 0xa0000000>;
        };

        fb: framebuffer@90000000 {
          reg = <0x0 0x90000000 0x0 0x00800000>;
          iommu-addresses = <&dc0 0x0 0x90000000 0x0 0x00800000>;
        };
      };

      bus@0 {
        #address-cells = <1>;
        #size-cells = <1>;
        ranges = <0x0 0x0 0x0 0x40000000>;

        adsp: adsp@2990000 {
          reg = <0x2990000 0x2000>;
          memory-region = <&adsp_resv>;
        };

        dc0: display@15200000 {
          reg = <0x15200000 0x10000>;
          memory-region = <&fb>;
        };
      };
    };
...