I have a Pi 4B 2G with a Uputronics u-blox GPS HAT, which puts the GPS module serial data on the first serial port lines. The problem is that U-Boot stops boot on serial input, and the GPS module is always sending data when it has a fix.
I put Fedora 36 Server on an SD card, and set the U-Boot stdin, stdout, and stderr environment variables to exclude serial (which wrote uboot.env), and that worked. Then I unplugged the keyboard... and it appeared to automatically re-add the serial and stop boot.
I have an extra Logitech unifying receiver I could leave plugged in (which seems to work), but that needlessly uses up a USB port. Is there a way to tell U-Boot "no really, ignore input from the serial port"?