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cpufreq: intel_pstate: Avoid enabling HWP if EPP is not supported

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Although there are processors supporting hardware-managed P-states
(HWP) without the energy-performance preference (EPP) feature, they
are not expected to be run with HWP enabled (the BIOS should disable
HWP on those systems).  Missing EPP support generally indicates an
incomplete HWP implementation and so it is better to avoid using
HWP on those systems in production.

However, intel_pstate currently enables HWP on such systems, which
is questionable, so prevent it from doing that by making it check
EPP support before enabling HWP and avoid enabling it if EPP is not
supported by the processor at hand.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
This commit is contained in:
Rafael J. Wysocki 2020-07-14 20:17:24 +02:00
parent 23a522e388
commit 7aa1031223
1 changed files with 6 additions and 1 deletions
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7
drivers/cpufreq/intel_pstate.c
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@ -2823,7 +2823,12 @@ static int __init intel_pstate_init(void)
id = x86_match_cpu(hwp_support_ids);
if (id) {
copy_cpu_funcs(&core_funcs);
if (!no_hwp) {
/*
* Avoid enabling HWP for processors without EPP support,
* because that means incomplete HWP implementation which is a
* corner case and supporting it is generally problematic.
*/
if (!no_hwp && boot_cpu_has(X86_FEATURE_HWP_EPP)) {
hwp_active++;
hwp_mode_bdw = id->driver_data;
intel_pstate.attr = hwp_cpufreq_attrs;