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 <[e-mail]>
Suggested-by: Srinivas Pandruvada <[e-mail]>
Signed-off-by: Yu Chen <[e-mail]>
[ rjw: Subject/changelog, minor modifications ]
Signed-off-by: Rafael J. Wysocki <[e-mail]>

drivers/cpufreq/intel_pstate.c

···
 	return 0;
 }
 
+static void intel_pstate_hwp_enable(struct cpudata *cpudata);
+
 static int intel_pstate_resume(struct cpufreq_policy *policy)
 {
 	if (!hwp_active)
 		return 0;
 
 	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);