cpufreq: intel_pstate: Force HWP min perf before offline

Force HWP Request MAX = HWP Request MIN = HWP Capability MIN and EPP to
0xFF. In this way the performance limits on the offlined CPU will not
influence performance limits on its sibling CPU, which is still online.

If the sibling CPU is calling for higher performance, it will impact the
max core performance. Here core performance will follow higher of the
performance requests from each sibling.

Reported-and-tested-by: Chen Yu <[e-mail]>
Signed-off-by: Srinivas Pandruvada <[e-mail]>
Signed-off-by: Rafael J. Wysocki <[e-mail]>

drivers/cpufreq/intel_pstate.c

···
 	wrmsrl_on_cpu(cpu, MSR_HWP_REQUEST, value);
 }
 
+static void intel_pstate_hwp_force_min_perf(int cpu)
+{
+	u64 value;
+	int min_perf;
+
+	value = all_cpu_data[cpu]->hwp_req_cached;
+	value &= ~GENMASK_ULL(31, 0);
+	min_perf = HWP_LOWEST_PERF(all_cpu_data[cpu]->hwp_cap_cached);
+
+	/* Set hwp_max = hwp_min */
+	value |= HWP_MAX_PERF(min_perf);
+	value |= HWP_MIN_PERF(min_perf);
+
+	/* Set EPP/EPB to min */
+	if (static_cpu_has(X86_FEATURE_HWP_EPP))
+		value |= HWP_ENERGY_PERF_PREFERENCE(HWP_EPP_POWERSAVE);
+	else
+		intel_pstate_set_epb(cpu, HWP_EPP_BALANCE_POWERSAVE);
+
+	wrmsrl_on_cpu(cpu, MSR_HWP_REQUEST, value);
+}
+
 static int intel_pstate_hwp_save_state(struct cpufreq_policy *policy)
 {
 	struct cpudata *cpu_data = all_cpu_data[policy->cpu];
···
 	pr_debug("CPU %d exiting\n", policy->cpu);
 
 	intel_pstate_clear_update_util_hook(policy->cpu);
-	if (hwp_active)
+	if (hwp_active) {
 		intel_pstate_hwp_save_state(policy);
-	else
+		intel_pstate_hwp_force_min_perf(policy->cpu);
+	} else {
 		intel_cpufreq_stop_cpu(policy);
+	}
 }
 
 static int intel_pstate_cpu_exit(struct cpufreq_policy *policy)