PM: EM: Refactor em_pd_get_efficient_state() to be more flexible

The Energy Model (EM) is going to support runtime modification. There
are going to be 2 EM tables which store information. This patch aims
to prepare the code to be generic and use one of the tables. The function
will no longer get a pointer to 'struct em_perf_domain' (the EM) but
instead a pointer to 'struct em_perf_state' (which is one of the EM's
tables).

Prepare em_pd_get_efficient_state() for the upcoming changes and
make it possible to be re-used. Return an index for the best performance
state for a given EM table. The function arguments that are introduced
should allow to work on different performance state arrays. The caller of
em_pd_get_efficient_state() should be able to use the index either
on the default or the modifiable EM table.
Reviewed-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Reviewed-by: Hongyan Xia <hongyan.xia2@arm.com>
Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Tested-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Signed-off-by: Lukasz Luba <lukasz.luba@arm.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

include/linux/energy_model.h

@@ -175,33 +175,35 @@ void em_dev_unregister_perf_domain(struct device *dev);
 
 /**
  * em_pd_get_efficient_state() - Get an efficient performance state from the EM
- * @pd   : Performance domain for which we want an efficient frequency
- * @freq : Frequency to map with the EM
+ * @table:		List of performance states, in ascending order
+ * @nr_perf_states:	Number of performance states
+ * @freq:		Frequency to map with the EM
+ * @pd_flags:		Performance Domain flags
  *
  * It is called from the scheduler code quite frequently and as a consequence
  * doesn't implement any check.
  *
- * Return: An efficient performance state, high enough to meet @freq
+ * Return: An efficient performance state id, high enough to meet @freq
  * requirement.
  */
-static inline
-struct em_perf_state *em_pd_get_efficient_state(struct em_perf_domain *pd,
-						unsigned long freq)
+static inline int
+em_pd_get_efficient_state(struct em_perf_state *table, int nr_perf_states,
+			  unsigned long freq, unsigned long pd_flags)
 {
 	struct em_perf_state *ps;
 	int i;
 
-	for (i = 0; i < pd->nr_perf_states; i++) {
-		ps = &pd->table[i];
+	for (i = 0; i < nr_perf_states; i++) {
+		ps = &table[i];
 		if (ps->frequency >= freq) {
-			if (pd->flags & EM_PERF_DOMAIN_SKIP_INEFFICIENCIES &&
+			if (pd_flags & EM_PERF_DOMAIN_SKIP_INEFFICIENCIES &&
 			    ps->flags & EM_PERF_STATE_INEFFICIENT)
 				continue;
-			break;
+			return i;
 		}
 	}
 
-	return ps;
+	return nr_perf_states - 1;
 }
 
 /**
@@ -226,7 +228,7 @@ static inline unsigned long em_cpu_energy(struct em_perf_domain *pd,
 {
 	unsigned long freq, ref_freq, scale_cpu;
 	struct em_perf_state *ps;
-	int cpu;
+	int cpu, i;
 
 	if (!sum_util)
 		return 0;
@@ -250,7 +252,9 @@ static inline unsigned long em_cpu_energy(struct em_perf_domain *pd,
 	 * Find the lowest performance state of the Energy Model above the
 	 * requested frequency.
 	 */
-	ps = em_pd_get_efficient_state(pd, freq);
+	i = em_pd_get_efficient_state(pd->table, pd->nr_perf_states, freq,
+				      pd->flags);
+	ps = &pd->table[i];
 
 	/*
 	 * The capacity of a CPU in the domain at the performance state (ps)