cpufreq: intel_pstate: Avoid enabling HWP if EPP is not supported
diff mbox series

Message ID 1776084.Fkt4dJnx8e@kreacher
State Accepted
Commit 7aa1031223bc01483e7aca6b7838598c4edc19f4
Headers show
  • cpufreq: intel_pstate: Avoid enabling HWP if EPP is not supported
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Commit Message

Rafael J. Wysocki July 14, 2020, 6:17 p.m. UTC
From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

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>
 drivers/cpufreq/intel_pstate.c |    7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff mbox series

Index: linux-pm/drivers/cpufreq/intel_pstate.c
--- linux-pm.orig/drivers/cpufreq/intel_pstate.c
+++ linux-pm/drivers/cpufreq/intel_pstate.c
@@ -2899,7 +2899,12 @@  static int __init intel_pstate_init(void
 	id = x86_match_cpu(hwp_support_ids);
 	if (id) {
-		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_mode_bdw = id->driver_data;
 			intel_pstate.attr = hwp_cpufreq_attrs;