QEMU virt Armv8-A
=================

Trusted Firmware-A (TF-A) implements the EL3 firmware layer for QEMU virt
Armv8-A. BL1 is used as the BootROM, supplied with the -bios argument.
When QEMU starts all CPUs are released simultaneously, BL1 selects a
primary CPU to handle the boot and the secondaries are placed in a polling
loop to be released by normal world via PSCI.

BL2 edits the Flattened Device Tree, FDT, generated by QEMU at run-time to
add a node describing PSCI and also enable methods for the CPUs.

If ``ARM_LINUX_KERNEL_AS_BL33`` is set to 1 then this FDT will be passed to BL33
via register x0, as expected by a Linux kernel. This allows a Linux kernel image
to be booted directly as BL33 rather than using a bootloader.

An ARM64 defconfig v5.5 Linux kernel is known to boot, FDT doesn't need to be
provided as it's generated by QEMU.

Current limitations:

-  Only cold boot is supported
-  No build instructions for QEMU\_EFI.fd and rootfs-arm64.cpio.gz
-  No instructions for how to load a BL32 (Secure Payload)

``QEMU_EFI.fd`` can be dowloaded from
http://snapshots.linaro.org/components/kernel/leg-virt-tianocore-edk2-upstream/latest/QEMU-KERNEL-AARCH64/RELEASE_GCC5/QEMU_EFI.fd

Boot binaries, except BL1, are primarily loaded via semi-hosting so all
binaries has to reside in the same directory as QEMU is started from. This
is conveniently achieved with symlinks the local names as:

-  ``bl2.bin`` -> BL2
-  ``bl31.bin`` -> BL31
-  ``bl33.bin`` -> BL33 (``QEMU_EFI.fd``)
-  ``Image`` -> linux/arch/arm64/boot/Image

To build:

.. code:: shell

    make CROSS_COMPILE=aarch64-none-elf- PLAT=qemu

To start (QEMU v4.1.0):

.. code:: shell

    qemu-system-aarch64 -nographic -machine virt,secure=on -cpu cortex-a57  \
        -kernel Image                           \
        -append "console=ttyAMA0,38400 keep_bootcon root=/dev/vda2"   \
        -initrd rootfs-arm64.cpio.gz -smp 2 -m 1024 -bios bl1.bin   \
        -d unimp -semihosting-config enable,target=native