From: Rafael J. Wysocki Date: Tue, 14 Jul 2020 18:17:24 +0000 (+0200) Subject: cpufreq: intel_pstate: Avoid enabling HWP if EPP is not supported X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=7aa1031223bc;p=linux.git cpufreq: intel_pstate: Avoid enabling HWP if EPP is not supported 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 --- diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c index a394ff05aba62..482a5f241d1a4 100644 --- a/drivers/cpufreq/intel_pstate.c +++ b/drivers/cpufreq/intel_pstate.c @@ -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;