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
7 title: QEMU Firmware Configuration
8
9 maintainers:
10 - Rob Herring <robh@kernel.org>
11
12 description: |
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
27 properties:
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
41 required:
42 - compatible
43 - reg
44
45 additionalProperties: false
46
47 examples:
48 - |
49
50 fw-cfg@9020000 {
51 compatible = "qemu,fw-cfg-mmio";
52 reg = <0x9020000 0xa>;
53 };
54 ...
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