[coreboot] Porting to RS780/SB700 board

[Ed Swierk]

I'm attempting to port Coreboot to an Asus M4A78XTD board, which has
an RS780/SB700 chipset with a socket AM3 (Fam10h+DDR3) CPU.

Starting with the tilapia_10h mainboard code, the first problem I'm
hitting occurs very early on: any attempt to call pci_locate_device(),
for example in sb700_lpc_init(), hangs forever (or at least longer
than I'm willing to wait), unless I disable all the PCIe bridges on
the 780 by inserting the following into enable_rs780_dev8():

set_nbmisc_enable_bits(PCI_DEV(0, 0, 0), 0x0c, 0, 0x000300fc);

If I leave even one of the bridges enabled, I get the hang. See
section 2.5.6 in
http://support.amd.com/us/Embedded_TechDocs/43291_rs780_rpr_pub_1.01.pdf
for a description of this register.

With the PCIe bridges out of the picture, I get through memory
initialization (woo hoo!), but for some reason ram_fill() and
ram_verify() take many minutes to complete, and it hangs shortly
thereafter. Boot log attached.

Any clues would be appreciated!

--Ed