rpi: Compute Module 5 doesn't autoboot without debug UART

[Gijs Peskens]

I'm working on getting a compute module working with Yocto using U-Boot 
as bootloader, which mostly works thanks to previous work to get RPi 5 
working.
However I'm running into a strange issue: if I turn on the CM5 without 
the debug UART (which requires soldering a header onto the CM5) 
attached, the Pi doesn't boot beyond showing the submarine splash 
screen, if I boot it with the console attached it autoboots correctly.
If I attach the UART after the boot halted and press enter I get a 
U-Boot console, and giving the boot command boots it normally.
And setting bootdelay=-2 in the env allows it to correctly boot.

Which leads me to believe there is perhaps a spurious input registered 
by U-Boot which interrupts autobooting.

Is there a command that allows me to extract why U-Boot didn't continue 
autobooting?

And anyone have a hint how this could perhaps be fixed in a more elegant 
way (allowing interruptable autoboot).

The hardware I'm testing on is the CM5 devkit, I needed to make small 
changes to yocto to get it working:
https://github.com/agherzan/meta-raspberrypi/pull/1397

No changes were needed in U-Boot to get it to boot

Thanks,

Gijs