1# SPDX-License-Identifier: GPL-2.0 2%YAML 1.2 3--- 4$id: http://devicetree.org/schemas/firmware/qemu,fw-cfg-mmio.yaml# 5$schema: http://devicetree.org/meta-schemas/core.yaml# 6 7title: QEMU Firmware Configuration 8 9maintainers: 10 - Rob Herring <robh@kernel.org> 11 12description: | 13 Various QEMU emulation / virtualization targets provide the following 14 Firmware Configuration interface on the "virt" machine type: 15 16 - A write-only, 16-bit wide selector (or control) register, 17 - a read-write, 64-bit wide data register. 18 19 QEMU exposes the control and data register to guests as memory mapped 20 registers; their location is communicated to the guest's UEFI firmware in the 21 DTB that QEMU places at the bottom of the guest's DRAM. 22 23 The authoritative guest-side hardware interface documentation to the fw_cfg 24 device can be found in "docs/specs/fw_cfg.txt" in the QEMU source tree. 25 26 27properties: 28 compatible: 29 const: qemu,fw-cfg-mmio 30 31 reg: 32 maxItems: 1 33 description: | 34 * Bytes 0x0 to 0x7 cover the data register. 35 * Bytes 0x8 to 0x9 cover the selector register. 36 * Further registers may be appended to the region in case of future interface 37 revisions / feature bits. 38 39 dma-coherent: true 40 41required: 42 - compatible 43 - reg 44 45additionalProperties: false 46 47examples: 48 - | 49 50 fw-cfg@9020000 { 51 compatible = "qemu,fw-cfg-mmio"; 52 reg = <0x9020000 0xa>; 53 }; 54... 55