[coreboot] HT3 for AMD boards

Scott Duplichan scott at notabs.org
Mon Oct 25 22:53:03 CEST 2010


An HT configuration change is needed to allow the southbridge link
to run at HT3 frequencies on supported hardware. AMD family 10h
processors support HT3, as do many AMD motherboards. When the
southbridge runs at the default settings of 8-bit, 200 MHz, the
throughput is insufficient for supporting high resolution graphics.

I have the needed changes ready but can test only the mahogany_fam10
project. The change involves the buid swap list, which is also used
by projects supporting the previous generation AMD processor (family 0Fh).
The change may also allow family 0Fh boards to use improved SB link

Here is my proposal. If it seems OK, I will submit a patch.

1) Add an option for HT_MANUAL_SWAP_LIST to amdfam10/kconfig and 
   amdk8/kconfig. The default is zero, which means it has no effect
   unless overridden.
2) Modify ht_wrapper.c to use HT_MANUAL_SWAP_LIST as the swap list,
   if non-zero.
3) In mainboard/amd/mahogany_fam10/Kconfig, override HT_MANUAL_SWAP_LIST
   with the value that is known to allow HT3 to work.
4) Possibly do the same for mainboard/amd/mahogany/Kconfig and test
   using a family 0Fh processor (I think I can find one).
5) Modify amdht/comlib.h so that if a critical HT initialization error
   occurs, it is no longer ignored. It will now log a message such as:
   === Failure at line 1145 of file src/northbridge/amd/amdht/h3finit.c ===,
   though execution will continue for backwards compatibility.
The idea is that nothing changes by default, except for the one or two
projects I can test on real hardware. For other boards, owners of the
hardware can add the HT_MANUAL_SWAP_LIST override to their mainboard
kconfig and tweak it until it works.


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