PM: EM: Add em_dev_compute_costs()

The device drivers can modify EM at runtime by providing a new EM table.
The EM is used by the EAS and the em_perf_state::cost stores
pre-calculated value to avoid overhead. This patch provides the API for
device drivers to calculate the cost values properly (and not duplicate
the same code).

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>

Author: lukaszluba-arm

include/linux/energy_model.h

@@ -170,6 +170,8 @@ int em_dev_register_perf_domain(struct device *dev, unsigned int nr_states,
 void em_dev_unregister_perf_domain(struct device *dev);
 struct em_perf_table __rcu *em_table_alloc(struct em_perf_domain *pd);
 void em_table_free(struct em_perf_table __rcu *table);
+int em_dev_compute_costs(struct device *dev, struct em_perf_state *table,
+			 int nr_states);
 
 /**
  * em_pd_get_efficient_state() - Get an efficient performance state from the EM
@@ -379,6 +381,12 @@ struct em_perf_state *em_perf_state_from_pd(struct em_perf_domain *pd)
 {
 	return NULL;
 }
+static inline
+int em_dev_compute_costs(struct device *dev, struct em_perf_state *table,
+			 int nr_states)
+{
+	return -EINVAL;
+}
 #endif
 
 #endif

kernel/power/energy_model.c

@@ -276,6 +276,24 @@ static int em_compute_costs(struct device *dev, struct em_perf_state *table,
 	return 0;
 }
 
+/**
+ * em_dev_compute_costs() - Calculate cost values for new runtime EM table
+ * @dev		: Device for which the EM table is to be updated
+ * @table	: The new EM table that is going to get the costs calculated
+ *
+ * Calculate the em_perf_state::cost values for new runtime EM table. The
+ * values are used for EAS during task placement. It also calculates and sets
+ * the efficiency flag for each performance state. When the function finish
+ * successfully the EM table is ready to be updated and used by EAS.
+ *
+ * Return 0 on success or a proper error in case of failure.
+ */
+int em_dev_compute_costs(struct device *dev, struct em_perf_state *table,
+			 int nr_states)
+{
+	return em_compute_costs(dev, table, NULL, nr_states, 0);
+}
+
 /**
  * em_dev_update_perf_domain() - Update runtime EM table for a device
  * @dev		: Device for which the EM is to be updated