I planned to test coreboot on this board as well, and I'm having the same problem
(compiled from latest source).
The sticks I currently have are 16GB VLP ones. I've some M392B2G70DM0-YK0, and a few
HMT42GR7AFR4A-PB. None worked with this board using coreboot, giving out similar
"DIMM training failed" message on the serial console output.
All those RAM sticks work on stock BIOS. Just that the board would run them at 1066MHz if
all 8 slots are populated (M392B2G70DM0-YK0 for example). Not sure if this is due to
incompatibility or is a chipset limitation (manually setting it to 1600MHz in stock BIOS
has no effect if using 8 sticks). If only using 4 sticks (which makes 64GB) with stock
BIOS, the memory can correctly operate at 1600MHz. Still, none of the combinations (2, 4,
8 sticks) worked with coreboot.
Is there a way to manually force memory clock and timing configuration (such as 1066MHz)
for some in-depth testing? On the other hand, I might need to test libreboot to see if it
makes a difference, and check for nearby coreboot commits to look for a starting point for