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Diffstat (limited to 'doc/develop')
| -rw-r--r-- | doc/develop/devicetree/dt_qemu.rst | 48 | ||||
| -rw-r--r-- | doc/develop/devicetree/index.rst | 1 |
2 files changed, 49 insertions, 0 deletions
diff --git a/doc/develop/devicetree/dt_qemu.rst b/doc/develop/devicetree/dt_qemu.rst new file mode 100644 index 0000000..c25c4fb --- /dev/null +++ b/doc/develop/devicetree/dt_qemu.rst @@ -0,0 +1,48 @@ +.. SPDX-License-Identifier: GPL-2.0+ + +Devicetree in QEMU +================== + +For QEMU on ARM, RISC-V and one PPC target, the devicetree is created on-the-fly +by QEMU. It is intended for use in Linux but can be used by U-Boot also, so long +as any nodes/properties needed by U-Boot are merged in. + +When `CONFIG_OF_BOARD` is enabled + + +Obtaining the QEMU devicetree +----------------------------- + +Where QEMU generates its own devicetree to pass to U-Boot tou can use +`-dtb u-boot.dtb` to force QEMU to use U-Boot's in-tree version. + +To obtain the devicetree that qemu generates, add `-machine dumpdtb=qemu.dtb`, +e.g.:: + + qemu-system-arm -machine virt -machine dumpdtb=qemu.dtb + + qemu-system-aarch64 -machine virt -machine dumpdtb=qemu.dtb + + qemu-system-riscv64 -machine virt -machine dumpdtb=qemu.dtb + + +Merging in U-Boot nodes/properties +---------------------------------- + +Various U-Boot features require nodes and properties in the U-Boot devicetree +and at present QEMU is unaware of these. To use these you must manually merge +in the appropriate pieces. + +One way to do this is with dtc. This command runs dtc on each .dtb file in turn, +to produce a text file. It drops the duplicate header on the qemu one. Then it +joins them up and runs them through dtc to compile the output:: + + qemu-system-arm -machine virt -machine dumpdtb=qemu.dtb + cat <(dtc -I dtb qemu.dtb) <(dtc -I dtb u-boot.dtb |grep -v /dts-v1/) |dtc - -o merged.dtb + +You can then run qemu with the merged devicetree, e.g.:: + + qemu-system-arm -machine virt -nographic -bios u-boot.bin -dtb merged.dtb + +Note that there seems to be a bug in some versions of qemu where the output of +dumpdtb does not quite match what is provided to U-Boot. diff --git a/doc/develop/devicetree/index.rst b/doc/develop/devicetree/index.rst index fa5db3e..2edb695 100644 --- a/doc/develop/devicetree/index.rst +++ b/doc/develop/devicetree/index.rst @@ -11,3 +11,4 @@ build-time and runtime configuration. intro control + dt_qemu |