config.txt

[pi3]
kernel=u-boot-rpi3.bin

[pi4]
kernel=u-boot-rpi4.bin
enable_gic=1
armstub=armstub8-gic.bin

# Otherwise the resolution will be weird in most cases, compared to
# what the pi3 firmware does by default.
disable_overscan=1

[all]
# Boot in 64-bit mode.
arm_64bit=1

# U-Boot needs this to work, regardless of whether UART is actually used or not.
# Look in arch/arm/mach-bcm283x/Kconfig in the U-Boot tree to see if this is still
# a requirement in the future.
enable_uart=1

# Prevent the firmware from smashing the framebuffer setup done by the mainline kernel
# when attempting to show low-voltage or overtemperature warnings.
avoid_warnings=1