#
  # Copyright (C) 2017, Tuomas Tynkkynen <tuomas.tynkkynen@iki.fi>
  #
  # SPDX-License-Identifier:	GPL-2.0+
  #

  U-Boot on QEMU's 'virt' machine on ARM & AArch64
  ================================================

  
  QEMU for ARM supports a special 'virt' machine designed for emulation and
  virtualization purposes. This document describes how to run U-Boot under it.

  Both 32-bit ARM and AArch64 are supported.

  
  The 'virt' platform provides the following as the basic functionality:
  
      - A freely configurable amount of CPU cores
      - U-Boot loaded and executing in the emulated flash at address 0x0
      - A generated device tree blob placed at the start of RAM
      - A freely configurable amount of RAM, described by the DTB
      - A PL011 serial port, discoverable via the DTB

      - An ARMv7/ARMv8 architected timer

      - PSCI for rebooting the system
      - A generic ECAM-based PCI host controller, discoverable via the DTB
  
  Additionally, a number of optional peripherals can be added to the PCI bus.
  
  Building U-Boot
  ---------------

  Set the CROSS_COMPILE environment variable as usual, and run:

  - For ARM:

      make qemu_arm_defconfig
      make

  - For AArch64:
      make qemu_arm64_defconfig
      make

  Running U-Boot
  --------------
  The minimal QEMU command line to get U-Boot up and running is:

  - For ARM:

      qemu-system-arm -machine virt,highmem=off -bios u-boot.bin

  - For AArch64:
      qemu-system-aarch64 -machine virt,highmem=off -cpu cortex-a57 -bios u-boot.bin

  The 'highmem=off' parameter to the 'virt' machine is required for PCI to work

  in U-Boot. Also, for some odd reason qemu-system-aarch64 needs to be explicitly
  told to use a 64-bit CPU or it will boot in 32-bit mode.

  
  Additional peripherals that have been tested to work in both U-Boot and Linux
  can be enabled with the following command line parameters:
  
  - To add a Serial ATA disk via an Intel ICH9 AHCI controller, pass e.g.:
      -drive if=none,file=disk.img,id=mydisk -device ich9-ahci,id=ahci -device ide-drive,drive=mydisk,bus=ahci.0
  - To add an Intel E1000 network adapter, pass e.g.:
      -netdev user,id=net0 -device e1000,netdev=net0
  - To add an EHCI-compliant USB host controller, pass e.g.:
      -device usb-ehci,id=ehci
  - To add a NVMe disk, pass e.g.:
      -drive if=none,file=disk.img,id=mydisk -device nvme,drive=mydisk,serial=foo
  
  These have been tested in QEMU 2.9.0 but should work in at least 2.5.0 as well.