On Wed, Mar 16, 2016 at 03:52:28PM +0100, Rafael J. Wysocki wrote:

+/**
+ * cpufreq_enable_fast_switch - Enable fast frequency switching for policy.
+ * @policy: cpufreq policy to enable fast frequency switching for.
+ *
+ * Try to enable fast frequency switching for @policy.
+ *
+ * The attempt will fail if there is at least one transition notifier registered
+ * at this point, as fast frequency switching is quite fundamentally at odds
+ * with transition notifiers.  Thus if successful, it will make registration of
+ * transition notifiers fail going forward.
+ *
+ * Call under policy->rwsem.

Nobody reads a comment..

+ */
+void cpufreq_enable_fast_switch(struct cpufreq_policy *policy)
+{

	lockdep_assert_held(&policy->rwsem);

While everybody complains when there's a big nasty splat in their dmesg
;-)

+	mutex_lock(&cpufreq_fast_switch_lock);
+	if (policy->fast_switch_possible && cpufreq_fast_switch_count >= 0) {
+		cpufreq_fast_switch_count++;
+		policy->fast_switch_enabled = true;
+	} else {
+		pr_warn("cpufreq: CPU%u: Fast freqnency switching not enabled\n",
+			policy->cpu);
+	}
+	mutex_unlock(&cpufreq_fast_switch_lock);
+}