---
 drivers/cpufreq/intel_pstate.c |   72 +++++++++++++++++++++++++++++++----------
 1 file changed, 56 insertions(+), 16 deletions(-)

--- a/drivers/cpufreq/intel_pstate.c
+++ b/drivers/cpufreq/intel_pstate.c
@@ -897,11 +897,19 @@ static ssize_t show_base_frequency(struc
 
 cpufreq_freq_attr_ro(base_frequency);
 
+enum hwp_cpufreq_attr_index {
+	HWP_BASE_FREQUENCY_INDEX = 0,
+	HWP_PERFORMANCE_PREFERENCE_INDEX,
+	HWP_PERFORMANCE_AVAILABLE_PREFERENCES_INDEX,
+	HWP_CPUFREQ_ATTR_COUNT,
+};
+
 static struct freq_attr *hwp_cpufreq_attrs[] = {
-	&energy_performance_preference,
-	&energy_performance_available_preferences,
-	&base_frequency,
-	NULL,
+	[HWP_BASE_FREQUENCY_INDEX] = &base_frequency,
+	[HWP_PERFORMANCE_PREFERENCE_INDEX] = &energy_performance_preference,
+	[HWP_PERFORMANCE_AVAILABLE_PREFERENCES_INDEX] =
+				&energy_performance_available_preferences,
+	[HWP_CPUFREQ_ATTR_COUNT] = NULL,
 };
 
 static bool no_cas __ro_after_init;
@@ -1370,6 +1378,9 @@ static void intel_pstate_hwp_offline(str
 #define POWER_CTL_EE_ENABLE	1
 #define POWER_CTL_EE_DISABLE	2
 
+/* Enable bit for Dynamic Efficiency Control (DEC) */
+#define POWER_CTL_DEC_ENABLE	27
+
 static int power_ctl_ee_state;
 
 static void set_power_ctl_ee_state(bool input)
@@ -3758,6 +3769,26 @@ static const struct x86_cpu_id intel_hyb
 	{}
 };
 
+static bool hwp_check_epp(void)
+{
+	if (boot_cpu_has(X86_FEATURE_HWP_EPP))
+		return true;
+
+	/* Without EPP support, don't expose EPP-related sysfs attributes. */
+	hwp_cpufreq_attrs[HWP_PERFORMANCE_PREFERENCE_INDEX] = NULL;
+	hwp_cpufreq_attrs[HWP_PERFORMANCE_AVAILABLE_PREFERENCES_INDEX] = NULL;
+
+	return false;
+}
+
+static bool hwp_check_dec(void)
+{
+	u64 power_ctl;
+
+	rdmsrq(MSR_IA32_POWER_CTL, power_ctl);
+	return !!(power_ctl & BIT(POWER_CTL_DEC_ENABLE));
+}
+
 static int __init intel_pstate_init(void)
 {
 	static struct cpudata **_all_cpu_data;
@@ -3778,23 +3809,32 @@ static int __init intel_pstate_init(void
 
 	id = x86_match_cpu(hwp_support_ids);
 	if (id) {
-		hwp_forced = intel_pstate_hwp_is_enabled();
+		bool epp_present = hwp_check_epp();
 
-		if (hwp_forced)
+		/*
+		 * If HWP is enabled already, there is no choice but to deal
+		 * with it.
+		 */
+		hwp_forced = intel_pstate_hwp_is_enabled();
+		if (hwp_forced) {
 			pr_info("HWP enabled by BIOS\n");
-		else if (no_load)
+			no_hwp = 0;
+		} else if (no_load) {
 			return -ENODEV;
+		} else if (!epp_present && !hwp_check_dec()) {
+			/*
+			 * Avoid enabling HWP for processors without EPP support
+			 * unless the Dynamic Efficiency Control (DEC) enable
+			 * bit (MSR_IA32_POWER_CTL, bit 27) is set because that
+			 * means incomplete HWP implementation which is a corner
+			 * case and supporting it is generally problematic.
+			 */
+			no_hwp = 1;
+		}
 
 		copy_cpu_funcs(&core_funcs);
-		/*
-		 * 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 HWP is enabled already, though, there is no choice but to
-		 * deal with it.
-		 */
-		if ((!no_hwp && boot_cpu_has(X86_FEATURE_HWP_EPP)) || hwp_forced) {
+
+		if (!no_hwp) {
 			hwp_active = true;
 			hwp_mode_bdw = id->driver_data;
 			intel_pstate.attr = hwp_cpufreq_attrs;