cpufreq: intel_pstate: Enable HWP during system resume on CPU0

When maxcpus=1 is in the kernel command line, the BP is responsible
for re-enabling the HWP - because currently only the APs invoke
intel_pstate_hwp_enable() during their online process - which might
put the system into unstable state after resume.

Fix this by enabling the HWP explicitly on BP during resume.
Reported-by: Doug Smythies <dsmythies@telus.net>
Suggested-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Signed-off-by: Yu Chen <yu.c.chen@intel.com>
[ rjw: Subject/changelog, minor modifications ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/cpufreq/intel_pstate.c

@@ -779,6 +779,8 @@ static int intel_pstate_hwp_save_state(struct cpufreq_policy *policy)
 	return 0;
 }
 
+static void intel_pstate_hwp_enable(struct cpudata *cpudata);
+
 static int intel_pstate_resume(struct cpufreq_policy *policy)
 {
 	if (!hwp_active)
@@ -786,6 +788,9 @@ static int intel_pstate_resume(struct cpufreq_policy *policy)
 
 	mutex_lock(&intel_pstate_limits_lock);
 
+	if (policy->cpu == 0)
+		intel_pstate_hwp_enable(all_cpu_data[policy->cpu]);
+
 	all_cpu_data[policy->cpu]->epp_policy = 0;
 	intel_pstate_hwp_set(policy->cpu);