[coreboot] Logging from within romstage? Problems initializing uart

[Hal Martin]

Hi all,

I have been asked to clean up my patch enabling SuperIO uart on the
intense-pc:
https://review.coreboot.org/#/c/coreboot/+/22737/

The SIO1007 is supposed to properly initialize the UART in the
sio1007_enable_uart_at(),
but when I call it nothing seems to happen and the uart doesn't end up in a
working state.

To diagnose why this isn't working, I want to add some logging statements
to sio1007_enable_uart_at(), but it seems that printk() doesn't work in
romstage because the cbmem region isn't yet allocated?

Can anyone provide some pointers for how I might add some debugging
statements while in romstage? It's really quite annoying because the uart
works if I duplicate some SuperIO code borrowed from an Intel board in
romstage.c, but if I rely entirely on the initialization code from sio1007,
I have no uart and nothing in the cbmem logs to help me diagnose why it's
failing.

Any tips you have would be appreciated. Having uart is extremely helpful
for debugging when making modifications to coreboot. Unfortunately my
problem involves uart, which makes it much more difficult for me to debug!

Thanks,
Hal