Enable serial debug console for Clevo P570WM

[segfault_bilibili]

I've been contacting an owner of Clevo P570WM. We have two final objectives:

1. Enable PCIe 3.0 (probably not feasible with software-level mod but still appealing)

2. Support 16GB SO-DIMM DDR3 modules.

Personally I think the second goal is definitely theoretically possible because there have been official BIOS upgrades from ASUS/MSI etc. It was just Clevo who didn't do the same thing for their P570WM.

I tried to compare some of those upgrades and then removed a "report error and goto fail" ("goto fail" is confirmed in experiment) logic in Clevo P570WM's BIOS. But unfortunately this is not as simple as that. It didn't work out.

I can see debug messages/strings appearing in the disassembly/decompiled pseudo C code. However I don't know where those debug messages go.

The owner of this machine has purchased a POST code diagnostic card but unfortunately that thing didn't seem to be compatible either.

I see the old post on techinferno discussing the 16GB memory issue, the last reply was probably written by prema, which said "the project is dead because we don't have Intel's source code" but I'm still willing to have one last try.

However I think I need a working debugging measure at least.

[segfault_bilibili]

With a very constrained debugging tool, the POST debug LED, I managed to make the system boot with 16GB SODIMM on ASRock X79 Extreme9. But there was still a problem that BIOS reports about 4 TB of RAM, which is obviously ridiculous. This can be workaround by bcdedit truncatememory but I want a more complete fix.

Today I got MRC serial debug log working on ASRock X79 Extreme9.

Coreboot is a good reference. Until yesterday I didn't realize I must enable serial port by programming Super IO control registers. The PCH LPC decode seems to be related but it doesn't seem to be needed to be changed.

After that I made a small patch so that the memory capacity problem seems to be fixed as well!