I think Myles was right, there is a i2c mux in this server that somehow multiplexes DIMM devices on the i2c bus. I was able to guess which i2c ports contain the DIMM info, and which port is the mux, then added the mux to devicetree.cb and the DIMM ports under it. Now I'm able to use memory from both CPU's, at least for the combination of DIMM's I have (2x2x1GB and 2x2x512MB).
I'm glad it worked out!
So I'm basically able to use these servers now. I would love to have ACPI and Cool'nQuiet of course, perhaps I'll try to do that later.
Thanks very much for all help! If you want me to commit the new mainboard to your svn repository let me know.
Yes, please. If you'll send your latest patch with a Signed-off-by: line, I'll take it from there.
Thanks, Myles