[coreboot] unstable AMD Fam10h boot

[Patrick Georgi]

Hi,

I have some issues with an Fam10h board here. Every once in a while,
boot fails with "FIXME! CPU Version unknown or not supported!". The CPU
Version mask that is calculated at the location the patch changes is
0x10efff. This value appears if the result of the cpuid call (or NB
probe) is 0xffffff (the highest 8 bits aren't counted in, it might be
0xffffffff, too)

Attached patch fixes the issue for me by retrying until a valid value is
returned, which indicates that this might be a timing or concurrency
issue.

I'd appreciate if someone with more knowledge of the AMD code could look
into this, as this potentially endless loop is not a real fix.

Patrick