[qhwudbebd]

Given serial access on an mt7981, you can usually use the UART recovery protocol to boot a bricked device entirely over serial, e.g. with https://github.com/981213/mtk_uartboot just run something like

  mtk_uartboot -s /dev/ttyS0 -a -p bl2.ram -f fip.img

This works even if atf and u-boot are corrupt on the device: it's part of the SoC's boot rom.

This is one of the things that makes the filogic routers nice to hack at, the other being that they're arm64 rather than something weird and legacy.