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It uses U-Boot, but you can use U-Boot to launch an EFI executable.

https://docs.u-boot.org/en/latest/board/thead/lpi4a.html https://docs.u-boot.org/en/latest/usage/cmd/bootefi.html

It can be both - uboot can emulate enough of EFI to start Linux.

AIUI Linux boot flow with this SoC goes

internal rom -> u-boot SPL --> opensbi --> u-boot --> Linux

In kernel config I see: CONFIG_EFI_STUB=y CONFIG_EFI=y

If that's what identifies it

That just defines what the Linux kernel will be able to do, it doesn't necessarily imply that the hardware is using UEFI for firmware to launch another bootloader or OS.