cpufreq: Add callback to register with energy model

Many cpufreq drivers register with the energy model for each policy and
do exactly the same thing. Follow the footsteps of thermal-cooling, to
get it done from the cpufreq core itself.

Provide a new callback, which will be called, if present, by the cpufreq
core at the right moment (more on that in the code's comment). Also
provide a generic implementation that uses dev_pm_opp_of_register_em().

This also allows us to register with the EM at a later point of time,
compared to ->init(), from where the EM core can access cpufreq policy
directly using cpufreq_cpu_get() type of helpers and perform other work,
like marking few frequencies inefficient, this will be done separately.
Reviewed-by: Quentin Perret <qperret@google.com>
Reviewed-by: Lukasz Luba <lukasz.luba@arm.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>

drivers/cpufreq/cpufreq.c

@@ -1491,6 +1491,19 @@ static int cpufreq_online(unsigned int cpu)
 		write_lock_irqsave(&cpufreq_driver_lock, flags);
 		list_add(&policy->policy_list, &cpufreq_policy_list);
 		write_unlock_irqrestore(&cpufreq_driver_lock, flags);
+
+		/*
+		 * Register with the energy model before
+		 * sched_cpufreq_governor_change() is called, which will result
+		 * in rebuilding of the sched domains, which should only be done
+		 * once the energy model is properly initialized for the policy
+		 * first.
+		 *
+		 * Also, this should be called before the policy is registered
+		 * with cooling framework.
+		 */
+		if (cpufreq_driver->register_em)
+			cpufreq_driver->register_em(policy);
 	}
 
 	ret = cpufreq_init_policy(policy);

include/linux/cpufreq.h

@@ -9,10 +9,12 @@
 #define _LINUX_CPUFREQ_H
 
 #include <linux/clk.h>
+#include <linux/cpu.h>
 #include <linux/cpumask.h>
 #include <linux/completion.h>
 #include <linux/kobject.h>
 #include <linux/notifier.h>
+#include <linux/pm_opp.h>
 #include <linux/pm_qos.h>
 #include <linux/spinlock.h>
 #include <linux/sysfs.h>
@@ -373,6 +375,12 @@ struct cpufreq_driver {
 	/* platform specific boost support code */
 	bool		boost_enabled;
 	int		(*set_boost)(struct cpufreq_policy *policy, int state);
+
+	/*
+	 * Set by drivers that want to register with the energy model after the
+	 * policy is properly initialized, but before the governor is started.
+	 */
+	void		(*register_em)(struct cpufreq_policy *policy);
 };
 
 /* flags */
@@ -1046,4 +1054,10 @@ unsigned int cpufreq_generic_get(unsigned int cpu);
 void cpufreq_generic_init(struct cpufreq_policy *policy,
 		struct cpufreq_frequency_table *table,
 		unsigned int transition_latency);
+
+static inline void cpufreq_register_em_with_opp(struct cpufreq_policy *policy)
+{
+	dev_pm_opp_of_register_em(get_cpu_device(policy->cpu),
+				  policy->related_cpus);
+}
 #endif /* _LINUX_CPUFREQ_H */