I have a couple of Raspberry Pi 4Bs with a couple of different GPS HATs.
Both GPS HATs work similar - they use the main serial port pins to
transmit the NMEA sentences, several every second once they have GPS
sync. Since u-boot stops on serial input, this keeps them from booting
unattended.
With a fresh Fedora 41 install, I see u-boot start and then get the EFI
boot menu, which stops until I hit ENTER when the GPS HAT is attached.
I tried setting bootdelay to -2 but that seems to stop the EFI boot menu
from autobooting no matter what (e.g. pulled the HAT off and it still
stopped there).
I also changed stdin/stdout/stderr to remove serial, that didn't seem to
have any effect.
I assume people don't have these problems with the "official" Raspberry
Pi OS - do they build u-boot with different options from Fedora that
allow fully disabling the u-boot serial console mode?
--
Chris Adams <linux(a)cmadams.net>