1.. SPDX-License-Identifier: GPL-2.0+
2
3Devicetree in QEMU
4==================
5
6For QEMU on ARM, RISC-V and one PPC target, the devicetree is created on-the-fly
7by QEMU. It is intended for use in Linux but can be used by U-Boot also, so long
8as any nodes/properties needed by U-Boot are merged in.
9
10When `CONFIG_OF_BOARD` is enabled
11
12
13Obtaining the QEMU devicetree
14-----------------------------
15
16Where QEMU generates its own devicetree to pass to U-Boot you can use
17`-dtb u-boot.dtb` to force QEMU to use U-Boot's in-tree version.
18
19To obtain the devicetree that qemu generates, add `-machine dumpdtb=qemu.dtb`,
20e.g.::
21
22    qemu-system-arm -machine virt -machine dumpdtb=qemu.dtb
23
24    qemu-system-aarch64 -machine virt -machine dumpdtb=qemu.dtb
25
26    qemu-system-riscv64 -machine virt -machine dumpdtb=qemu.dtb
27
28
29Merging in U-Boot nodes/properties
30----------------------------------
31
32Various U-Boot features require nodes and properties in the U-Boot devicetree
33and at present QEMU is unaware of these. To use these you must manually merge
34in the appropriate pieces.
35
36One way to do this is with dtc. This command runs dtc on each .dtb file in turn,
37to produce a text file. It drops the duplicate header on the qemu one. Then it
38joins them up and runs them through dtc to compile the output::
39
40    qemu-system-arm -machine virt -machine dumpdtb=qemu.dtb
41    cat  <(dtc -I dtb qemu.dtb) <(dtc -I dtb u-boot.dtb | grep -v /dts-v1/) | dtc - -o merged.dtb
42
43You can then run qemu with the merged devicetree, e.g.::
44
45    qemu-system-arm -machine virt -nographic -bios u-boot.bin -dtb merged.dtb
46
47Note that there seems to be a bug in some versions of qemu where the output of
48dumpdtb does not quite match what is provided to U-Boot.
49