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>
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@ -74,7 +74,11 @@ int x86_mtrr_check(void);
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/* ROM caching can be used after variable MTRRs are set up. Beware that
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* enabling CONFIG_CACHE_ROM will eat through quite a few MTRRs based on
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* one's IO hole size and WRCOMB resources. Be sure to check the console
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* log when enabling CONFIG_CACHE_ROM or adding WRCOMB resources. */
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* log when enabling CONFIG_CACHE_ROM or adding WRCOMB resources. Beware that
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* on CPUs with core-scoped MTRR registers such as hyperthreaded CPUs the
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* rom caching will be disabled if all threads run the MTRR code. Therefore,
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* one needs to call x86_mtrr_enable_rom_caching() after all threads of the
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* same core have run the MTRR code. */
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#if CONFIG_CACHE_ROM
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void x86_mtrr_enable_rom_caching(void);
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void x86_mtrr_disable_rom_caching(void);
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