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c3c1614537
QEMU currently generates a devicetree for use with U-Boot. Explain how to obtain it. Also explain how to merge it to produce a devicetree with the U-Boot features included. Signed-off-by: Simon Glass <sjg@chromium.org>
49 lines
1.7 KiB
ReStructuredText
49 lines
1.7 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0+
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Devicetree in QEMU
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==================
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For QEMU on ARM, RISC-V and one PPC target, the devicetree is created on-the-fly
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by QEMU. It is intended for use in Linux but can be used by U-Boot also, so long
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as any nodes/properties needed by U-Boot are merged in.
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When `CONFIG_OF_BOARD` is enabled
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Obtaining the QEMU devicetree
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-----------------------------
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Where QEMU generates its own devicetree to pass to U-Boot tou can use
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`-dtb u-boot.dtb` to force QEMU to use U-Boot's in-tree version.
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To obtain the devicetree that qemu generates, add `-machine dumpdtb=qemu.dtb`,
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e.g.::
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qemu-system-arm -machine virt -machine dumpdtb=qemu.dtb
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qemu-system-aarch64 -machine virt -machine dumpdtb=qemu.dtb
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qemu-system-riscv64 -machine virt -machine dumpdtb=qemu.dtb
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Merging in U-Boot nodes/properties
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----------------------------------
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Various U-Boot features require nodes and properties in the U-Boot devicetree
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and at present QEMU is unaware of these. To use these you must manually merge
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in the appropriate pieces.
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One way to do this is with dtc. This command runs dtc on each .dtb file in turn,
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to produce a text file. It drops the duplicate header on the qemu one. Then it
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joins them up and runs them through dtc to compile the output::
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qemu-system-arm -machine virt -machine dumpdtb=qemu.dtb
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cat <(dtc -I dtb qemu.dtb) <(dtc -I dtb u-boot.dtb |grep -v /dts-v1/) |dtc - -o merged.dtb
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You can then run qemu with the merged devicetree, e.g.::
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qemu-system-arm -machine virt -nographic -bios u-boot.bin -dtb merged.dtb
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Note that there seems to be a bug in some versions of qemu where the output of
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dumpdtb does not quite match what is provided to U-Boot.
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