xref: /kernel/linux/linux-6.6/Documentation/devicetree/bindings/firmware/qemu,fw-cfg-mmio.yaml

# SPDX-License-Identifier: GPL-2.0
%YAML 1.2
---
$id: http://devicetree.org/schemas/firmware/qemu,fw-cfg-mmio.yaml#
$schema: http://devicetree.org/meta-schemas/core.yaml#

title: QEMU Firmware Configuration

maintainers:
  - Rob Herring <robh@kernel.org>

description: |
  Various QEMU emulation / virtualization targets provide the following
  Firmware Configuration interface on the "virt" machine type:

  - A write-only, 16-bit wide selector (or control) register,
  - a read-write, 64-bit wide data register.

  QEMU exposes the control and data register to guests as memory mapped
  registers; their location is communicated to the guest's UEFI firmware in the
  DTB that QEMU places at the bottom of the guest's DRAM.

  The authoritative guest-side hardware interface documentation to the fw_cfg
  device can be found in "docs/specs/fw_cfg.txt" in the QEMU source tree.


properties:
  compatible:
    const: qemu,fw-cfg-mmio

  reg:
    maxItems: 1
    description: |
      * Bytes 0x0 to 0x7 cover the data register.
      * Bytes 0x8 to 0x9 cover the selector register.
      * Further registers may be appended to the region in case of future interface
        revisions / feature bits.

  dma-coherent: true

required:
  - compatible
  - reg

additionalProperties: false

examples:
  - |

    fw-cfg@9020000 {
        compatible = "qemu,fw-cfg-mmio";
        reg = <0x9020000 0xa>;
    };
...