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mtrr: add rom caching comment about hyperthreads 

Explicitly call out the effects of hyperthreads running the
MTRR code and its impact on the enablement of ROM caching.

Change-Id: I14b8f3fdc112340b8f483f2e554c5680576a8a7c
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: http://review.coreboot.org/3018
Tested-by: build bot (Jenkins)
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
This commit is contained in:
Aaron Durbin 2013-04-03 09:57:53 -05:00 committed by Stefan Reinauer
parent 0dc775e894
commit 6ccb1abfd4
1 changed files with 5 additions and 1 deletions
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6
src/include/cpu/x86/mtrr.h
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@ -74,7 +74,11 @@ int x86_mtrr_check(void);
/* ROM caching can be used after variable MTRRs are set up. Beware that
* enabling CONFIG_CACHE_ROM will eat through quite a few MTRRs based on
* one's IO hole size and WRCOMB resources. Be sure to check the console
* log when enabling CONFIG_CACHE_ROM or adding WRCOMB resources. */
* log when enabling CONFIG_CACHE_ROM or adding WRCOMB resources. Beware that
* on CPUs with core-scoped MTRR registers such as hyperthreaded CPUs the
* rom caching will be disabled if all threads run the MTRR code. Therefore,
* one needs to call x86_mtrr_enable_rom_caching() after all threads of the
* same core have run the MTRR code. */
#if CONFIG_CACHE_ROM
void x86_mtrr_enable_rom_caching(void);
void x86_mtrr_disable_rom_caching(void);