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authorDirk Brandewie <dirk.j.brandewie@intel.com>2014-06-20 07:27:59 -0700
committerRafael J. Wysocki <rafael.j.wysocki@intel.com>2014-07-07 01:22:19 +0200
commitdd5fbf70f96dbfd7ee432096a1f979b2b3267856 (patch)
tree7829e15ad3cd4dbdbdd1121f4d7649bf008f6481 /Documentation/cpu-freq
parentc16ed06024a6e699c332831dd50d8276744e3de8 (diff)
intel_pstate: don't touch turbo bit if turbo disabled or unavailable.
If turbo is disabled in the BIOS bit 38 should be set in MSR_IA32_MISC_ENABLE register per section 14.3.2.1 of the SDM Vol 3 document 325384-050US Feb 2014. If this bit is set do *not* attempt to disable trubo via the MSR_IA32_PERF_CTL register. On some systems trying to disable turbo via MSR_IA32_PERF_CTL will cause subsequent writes to MSR_IA32_PERF_CTL not take affect, in fact reading MSR_IA32_PERF_CTL will not show the IDA/Turbo DISENGAGE bit(32) as set. A write of bit 32 to zero returns to normal operation. Also deal with the case where the processor does not support turbo and the BIOS does not report the fact in MSR_IA32_MISC_ENABLE but does report the max and turbo P states as the same value. Link: https://bugzilla.kernel.org/show_bug.cgi?id=64251 Cc: 3.13+ <stable@vger.kernel.org> # 3.13+ Signed-off-by: Dirk Brandewie <dirk.j.brandewie@intel.com> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
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