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 ---
Changes in v5: - Merge RISC-V and ARM patches since they are similar
doc/board/emulation/qemu-arm.rst | 3 ++ doc/board/emulation/qemu-riscv.rst | 3 ++ doc/develop/devicetree/dt_qemu.rst | 48 ++++++++++++++++++++++++++++++ doc/develop/devicetree/index.rst | 1 + 4 files changed, 55 insertions(+) create mode 100644 doc/develop/devicetree/dt_qemu.rst
diff --git a/doc/board/emulation/qemu-arm.rst b/doc/board/emulation/qemu-arm.rst index 97b6ec64905..a39df046fc3 100644 --- a/doc/board/emulation/qemu-arm.rst +++ b/doc/board/emulation/qemu-arm.rst @@ -21,6 +21,9 @@ The 'virt' platform provides the following as the basic functionality:
Additionally, a number of optional peripherals can be added to the PCI bus.
+See :doc:`../../develop/devicetree/dt_qemu` for information on how to see +the devicetree actually generated by QEMU. + Building U-Boot --------------- Set the CROSS_COMPILE environment variable as usual, and run: diff --git a/doc/board/emulation/qemu-riscv.rst b/doc/board/emulation/qemu-riscv.rst index 4b8e104a215..3409fff8117 100644 --- a/doc/board/emulation/qemu-riscv.rst +++ b/doc/board/emulation/qemu-riscv.rst @@ -13,6 +13,9 @@ The QEMU virt machine models a generic RISC-V virtual machine with support for the VirtIO standard networking and block storage devices. It has CLINT, PLIC, 16550A UART devices in addition to VirtIO and it also uses device-tree to pass configuration information to guest software. It implements RISC-V privileged + +See :doc:`../../develop/devicetree/dt_qemu` for information on how to see +the devicetree actually generated by QEMU. architecture spec v1.10.
Building U-Boot diff --git a/doc/develop/devicetree/dt_qemu.rst b/doc/develop/devicetree/dt_qemu.rst new file mode 100644 index 00000000000..1392a2cae97 --- /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 b5b33dfea0f..fc2fb41b1bb 100644 --- a/doc/develop/devicetree/index.rst +++ b/doc/develop/devicetree/index.rst @@ -12,3 +12,4 @@ build-time and runtime configuration. intro control dt_update + dt_qemu