New patch to review for coreboot: 5ec50ef mtrr: add rom caching comment about hyperthreads

[Aaron Durbin]

Aaron Durbin ([e-mail]) just uploaded a new patch set to gerrit, which you can find at http://review.coreboot.org/3018

-gerrit

commit 5ec50ef9f0339df0bae1fd2185e31153ae439a48
Author: Aaron Durbin 
Date:   Wed Apr 3 09:57:53 2013 -0500

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 
---
 src/include/cpu/x86/mtrr.h | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/src/include/cpu/x86/mtrr.h b/src/include/cpu/x86/mtrr.h
index 15a5cad..747c1e9 100644
--- a/src/include/cpu/x86/mtrr.h
+++ b/src/include/cpu/x86/mtrr.h
@@ -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 thread 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);