pm: policy: return a reference to the next state

Return a constant reference to the next state instead of a copy of
struct pm_state_info. When the next state should be active, just return
NULL. Struct copying should be in general avoided, specially in code
paths executed frequently as is this one.

Signed-off-by: Gerard Marull-Paretas <gerard.marull@nordicsemi.no>

include/pm/policy.h

@@ -26,9 +26,10 @@ extern "C" {
  * @param cpu CPU index.
  * @param ticks The number of ticks to the next scheduled event.
  *
- * @return The power state the system should use for the given cpu.
+ * @return The power state the system should use for the given cpu. The function
+ * will return NULL if system should remain into PM_STATE_ACTIVE.
  */
-struct pm_state_info pm_policy_next_state(uint8_t cpu, int32_t ticks);
+const struct pm_state_info *pm_policy_next_state(uint8_t cpu, int32_t ticks);
 
 /** @endcond */
 

subsys/pm/pm.c

@@ -194,7 +194,12 @@ bool pm_system_suspend(int32_t ticks)
 	SYS_PORT_TRACING_FUNC_ENTER(pm, system_suspend, ticks);
 
 	if (!atomic_test_and_set_bit(z_power_states_forced, id)) {
-		z_power_states[id] = pm_policy_next_state(id, ticks);
+		const struct pm_state_info *info;
+
+		info = pm_policy_next_state(id, ticks);
+		if (info != NULL) {
+			z_power_states[id] = *info;
+		}
 	}
 
 	if (z_power_states[id].state == PM_STATE_ACTIVE) {

subsys/pm/policy/residency.c

@@ -12,7 +12,7 @@
 #include <logging/log.h>
 LOG_MODULE_DECLARE(pm, CONFIG_PM_LOG_LEVEL);
 
-struct pm_state_info pm_policy_next_state(uint8_t cpu, int32_t ticks)
+const struct pm_state_info *pm_policy_next_state(uint8_t cpu, int32_t ticks)
 {
 	uint8_t num_cpu_states;
 	const struct pm_state_info *cpu_states;
@@ -36,10 +36,10 @@ struct pm_state_info pm_policy_next_state(uint8_t cpu, int32_t ticks)
 				"(ticks: %d, min_residency: %u) to cpu %d",
 				state->state, ticks, state->min_residency_us,
 				cpu);
-			return *state;
+			return state;
 		}
 	}
 
 	LOG_DBG("No suitable power state found for cpu: %d!", cpu);
-	return (struct pm_state_info){PM_STATE_ACTIVE, 0, 0};
+	return NULL;
 }

tests/kernel/profiling/profiling_api/src/main.c

@@ -23,7 +23,7 @@ static void tdata_dump_callback(const struct k_thread *thread, void *user_data)
 }
 
 /* Our PM policy handler */
-struct pm_state_info pm_policy_next_state(uint8_t cpu, int32_t ticks)
+const struct pm_state_info *pm_policy_next_state(uint8_t cpu, int32_t ticks)
 {
 	static bool test_flag;
 
@@ -37,7 +37,7 @@ struct pm_state_info pm_policy_next_state(uint8_t cpu, int32_t ticks)
 		test_flag = true;
 	}
 
-	return (struct pm_state_info){PM_STATE_ACTIVE, 0, 0};
+	return NULL;
 }
 
 /*work handler*/

tests/subsys/pm/device_wakeup_api/src/main.c

@@ -57,16 +57,20 @@ void pm_power_state_exit_post_ops(struct pm_state_info info)
 	irq_unlock(0);
 }
 
-struct pm_state_info pm_policy_next_state(uint8_t cpu, int32_t ticks)
+const struct pm_state_info *pm_policy_next_state(uint8_t cpu, int32_t ticks)
 {
+	static const struct pm_state_info state = {
+		.state = PM_STATE_SUSPEND_TO_RAM
+	};
+
 	ARG_UNUSED(cpu);
 
 	while (sleep_count < 3) {
 		sleep_count++;
-		return (struct pm_state_info){PM_STATE_SUSPEND_TO_RAM, 0, 0, 0};
+		return &state;
 	}
 
-	return (struct pm_state_info){PM_STATE_ACTIVE, 0, 0, 0};
+	return NULL;
 }
 
 void test_wakeup_device_api(void)

tests/subsys/pm/power_mgmt/src/main.c

@@ -198,9 +198,9 @@ void pm_power_state_exit_post_ops(struct pm_state_info info)
 }
 
 /* Our PM policy handler */
-struct pm_state_info pm_policy_next_state(uint8_t cpu, int ticks)
+const struct pm_state_info *pm_policy_next_state(uint8_t cpu, int32_t ticks)
 {
-	struct pm_state_info info = {};
+	static struct pm_state_info info;
 
 	ARG_UNUSED(cpu);
 
@@ -219,7 +219,7 @@ struct pm_state_info pm_policy_next_state(uint8_t cpu, int ticks)
 		 */
 		info.state = PM_STATE_ACTIVE;
 	}
-	return info;
+	return &info;
 }
 
 /* implement in application, called by idle thread */

tests/subsys/pm/power_mgmt_multicore/src/main.c

@@ -60,9 +60,9 @@ void pm_power_state_exit_post_ops(struct pm_state_info info)
 	irq_unlock(0);
 }
 
-struct pm_state_info pm_policy_next_state(uint8_t cpu, int ticks)
+const struct pm_state_info *pm_policy_next_state(uint8_t cpu, int ticks)
 {
-	struct pm_state_info info = {};
+	static struct pm_state_info info = {};
 	int32_t msecs = k_ticks_to_ms_floor64(ticks);
 
 	if (msecs < ACTIVE_MSEC) {
@@ -81,7 +81,7 @@ struct pm_state_info pm_policy_next_state(uint8_t cpu, int ticks)
 
 	state_testing[_current_cpu->id] = info.state;
 
-	return info;
+	return &info;
 }
 
 /*