But I can't turn on the sercon port for boot
menu. Seems that address for
sercon is u16, only take 16bit address. I use 16bit serial port address
for coreboot 0x3e8, it is not working.
How to turn on MMIO serial console for boot menu?
Not supported right now. Needs non-trivial changes, sercon code might
have to switch to 32bit mode for mmio access, the registers are
out-of-reach in real mode.