[coreboot] How to improve the boot time of the Asus KGPE-D16?

[Paul Menzel]

Dear coreboot folks,

With 128 GB of RAM consisting of eight 16 GB modules, coreboot takes
over a minute to get to the payload on the Asus KGPE-D16 even without
serial console enabled [1]. This is not much faster than the vendor
firmware.

Please note that the timings below are incorrect. Comparing it with the
timings from SeaBIOS’ `script/read_serial.py`, I’d say the time values
need to be multiplied by two. (Somebody mentioned, that the reason
might be `cbmem -t` using some scaling factor to convert the time
stamps to seconds, and that might be wrong on the board.)

```
$ more asus/kgpe-d16/4.5-1093-g308aeff/2017-03-01T16_03_07Z/coreboot_timestamps.txt
21 entries total:

0:1st timestamp                                     24,384
   1:start of rom stage                                25,061 (676)
   2:before ram initialization                         913,502 (888,441)
   3:after ram initialization                          35,548,889 (34,635,386)
   4:end of romstage                                   35,642,960 (94,070)
   8:starting to load ramstage                         35,647,351 (4,391)
  15:starting LZMA decompress (ignore for x86)         35,647,872 (520)
  16:finished LZMA decompress (ignore for x86)         35,695,864 (47,991)
   9:finished loading ramstage                         35,696,312 (447)
  10:start of ramstage                                 35,696,893 (581)
  30:device enumeration                                35,696,897 (3)
  40:device configuration                              36,639,627 (942,730)
  50:device enable                                     36,644,848 (5,221)
  60:device initialization                             36,646,012 (1,163)
  70:device setup done                                 37,044,848 (398,836)
  75:cbmem post                                        37,044,850 (1)
  80:write tables                                      37,044,851 (1)
  85:finalize chips                                    37,053,950 (9,099)
  90:load payload                                      37,324,647 (270,697)
  15:starting LZMA decompress (ignore for x86)         37,325,042 (395)
  16:finished LZMA decompress (ignore for x86)         37,349,321 (24,278)
  99:selfboot jump                                     37,349,328 (7)
```

I think most of the time is spent in RAM initialization.

1. Do board owners with similar amount of memory (independent of the
      board) have similar numbers?
   2. What are the ways to improve that? Is it possible? For example, can
      the modules be probed in parallel (if that isn’t done already)?

Thanks,

Paul

[1] https://review.coreboot.org/cgit/board-status.git/commit/?id=4b4b7ab5865b15a...