[coreboot] [PATCH] Implement DIMM loading for DDR on K8

[Rudolf Marek]

Hello,

Attached patch implements the memory speed reductions (and 2T/1T clock logic) 
for DDR1 memory (939 sockets). The details can be found in BKDG chapter 4.1.3.3.

The patch looks at certain DDR configurations (dual rank/single rank) and lowers 
the clocks to 2T or frequency as guide suggest. It sets the DualDIMMen bit which 
I believe should be set for non-dual channel configs.

Dual DIMM Enable (DualDimmEn)—Bit 9. When this bit is set, the A copy of the 
memory address bus is enabled, regardless of the MC0_EN (Function 2, Offset 94h) 
value, and the B copy of the memory bus is disabled if 939 package with 128-bit 
bus is not used. This bit should be set if unbuffered DIMMs are used, and two 
DIMM sockets are connected to the A copy of the memory address bus, as in SODIMM 
or 939 package configurations. See “Register Differences in Revisions of the AMD 
AthlonTM 64.

The patch does not implement support for three dimm configurations supported 
from revE.

On the other hand it should improve greatly memory stability across the 939 
platform.

Signed-off-by: Rudolf Marek

Thanks,
Rudolf