boot/edk2: add support for RISC-V 64bit architecture

RISC-V 64bit qemu virt machine support has been added in edk2
version "stable202302". See [1].

Since edk2-stable202308, introduced in buildroot in commit 5c9f310
"boot/edk2: bump to version edk2-stable202308", it is now possible
to boot the edk2 UEFI shell in qemu.

This commit adds this early RISC-V support to edk2.

The RISC-V edk2 UEFI shell can be booted in Buildroot with the
following commands:

    # Build EDK2 images
    cat > .config <<EOF
    BR2_riscv=y
    BR2_RISCV_64=y
    BR2_PACKAGE_HOST_QEMU=y
    BR2_PACKAGE_HOST_QEMU_SYSTEM_MODE=y
    BR2_TARGET_EDK2=y
    EOF
    make olddefconfig
    make

    # edk2 image size should fit the 32MB of qemu pflash memories
    truncate -s 32M output/images/RISCV_VIRT_CODE.fd
    truncate -s 32M output/images/RISCV_VIRT_VARS.fd

    # Start qemu:
    output/host/usr/bin/qemu-system-riscv64 \
        -M virt,pflash0=pflash0,pflash1=pflash1,acpi=off \
        -nographic \
        -blockdev node-name=pflash0,driver=file,read-only=on,filename=output/images/RISCV_VIRT_CODE.fd \
        -blockdev node-name=pflash1,driver=file,filename=output/images/RISCV_VIRT_VARS.fd

Note: a Qemu version >= 8.0.0 is needed to properly start edk2. A qemu
version on the host system might not be sufficient. This is why the
Buildroot host-qemu is built in this config example.

[1] https://github.com/tianocore/edk2/releases/tag/edk2-stable202302

Signed-off-by: Julien Olivain <ju.o@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

boot/edk2/Config.in

@@ -2,6 +2,7 @@ config BR2_TARGET_EDK2_ARCH_SUPPORTS
 	bool
 	default y if BR2_aarch64
 	default y if BR2_i386
+	default y if BR2_RISCV_64
 	default y if BR2_x86_64
 
 config BR2_TARGET_EDK2
@@ -20,6 +21,7 @@ if BR2_TARGET_EDK2
 choice
 	prompt "Platform"
 	default BR2_TARGET_EDK2_PLATFORM_OVMF_I386 if BR2_i386
+	default BR2_TARGET_EDK2_PLATFORM_OVMF_RISCV if BR2_RISCV_64
 	default BR2_TARGET_EDK2_PLATFORM_OVMF_X64 if BR2_x86_64
 	default BR2_TARGET_EDK2_PLATFORM_ARM_VIRT_QEMU if BR2_aarch64
 
@@ -31,6 +33,14 @@ config BR2_TARGET_EDK2_PLATFORM_OVMF_I386
 	  This platform will boot from flash address 0x0.
 	  It should therefore be used as the first bootloader.
 
+config BR2_TARGET_EDK2_PLATFORM_OVMF_RISCV
+	bool "RISC-V"
+	depends on BR2_RISCV_64
+	help
+	  Platform configuration for RISC-V QEMU targeting the Virt
+	  machine. This platform will only boot from flash address
+	  0x0. It should therefore be used as the first bootloader.
+
 config BR2_TARGET_EDK2_PLATFORM_OVMF_X64
 	bool "x86-64"
 	depends on BR2_x86_64

boot/edk2/edk2.mk

@@ -136,6 +136,12 @@ define EDK2_PRE_BUILD_QEMU_SBSA
 	ln -srf $(BINARIES_DIR)/{bl1.bin,fip.bin} $(EDK2_BUILD_PACKAGES)/Platform/Qemu/Sbsa/
 endef
 
+else ifeq ($(BR2_TARGET_EDK2_PLATFORM_OVMF_RISCV),y)
+EDK2_ARCH = RISCV64
+EDK2_PACKAGE_NAME = OvmfPkg/RiscVVirt
+EDK2_PLATFORM_NAME = RiscVVirtQemu
+EDK2_BUILD_DIR = $(EDK2_PLATFORM_NAME)
+
 endif
 
 EDK2_BASETOOLS_OPTS = \