power: remove device_pm_control_nop function

Devices that do not require PM should just use NULL.
`device_pm_control_nop` is still kept as an alias to NULL untill all
in-tree usage is replaced with NULL.

Code relying on device_pm_control function now returns -ENOTSUP
(equivalent to calling device_pm_control_nop).

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

include/device.h

@@ -141,7 +141,7 @@ typedef int16_t device_handle_t;
  * @param init_fn Address to the init function of the driver.
  *
  * @param pm_control_fn Pointer to device_pm_control function.
- * Can be empty function (device_pm_control_nop) if not implemented.
+ * Can be NULL if not implemented.
  *
  * @param data_ptr Pointer to the device's private data.
  *
@@ -199,7 +199,7 @@ typedef int16_t device_handle_t;
  * @param init_fn Address to the init function of the driver.
  *
  * @param pm_control_fn Pointer to device_pm_control function.
- * Can be empty function (device_pm_control_nop) if not implemented.
+ * Can be NULL if not implemented.
  *
  * @param data_ptr Pointer to the device's private data.
  *
@@ -744,25 +744,6 @@ void device_busy_clear(const struct device *dev);
  * Device PM functions
  */
 
-/**
- * @brief No-op function to initialize unimplemented hook
- *
- * This function should be used to initialize device hook
- * for which a device has no PM operations.
- *
- * @param unused_device Unused
- * @param unused_ctrl_command Unused
- * @param unused_context Unused
- * @param cb Unused
- * @param unused_arg Unused
- *
- * @retval -ENOTSUP for all operations.
- */
-int device_pm_control_nop(const struct device *unused_device,
-			  uint32_t unused_ctrl_command,
-			  void *unused_context,
-			  device_pm_cb cb,
-			  void *unused_arg);
 /**
  * @brief Call the set power state function of a device
  *
@@ -781,15 +762,12 @@ static inline int device_set_power_state(const struct device *dev,
 					 uint32_t device_power_state,
 					 device_pm_cb cb, void *arg)
 {
-	if (dev->device_pm_control) {
+	if (dev->device_pm_control ==  NULL) {
-		return dev->device_pm_control(dev,
+		return -ENOSYS;
-						 DEVICE_PM_SET_POWER_STATE,
-						 &device_power_state, cb, arg);
-	} else {
-		return device_pm_control_nop(dev,
-						 DEVICE_PM_SET_POWER_STATE,
-						 &device_power_state, cb, arg);
 	}
+
+	return dev->device_pm_control(dev, DEVICE_PM_SET_POWER_STATE,
+				      &device_power_state, cb, arg);
 }
 
 /**
@@ -808,15 +786,12 @@ static inline int device_set_power_state(const struct device *dev,
 static inline int device_get_power_state(const struct device *dev,
 					 uint32_t *device_power_state)
 {
-	if (dev->device_pm_control) {
+	if (dev->device_pm_control == NULL) {
-		return dev->device_pm_control(dev,
+		return -ENOSYS;
-						 DEVICE_PM_GET_POWER_STATE,
-						 device_power_state, NULL, NULL);
-	} else {
-		return device_pm_control_nop(dev,
-						 DEVICE_PM_GET_POWER_STATE,
-						 device_power_state, NULL, NULL);
 	}
+
+	return dev->device_pm_control(dev, DEVICE_PM_GET_POWER_STATE,
+				      device_power_state, NULL, NULL);
 }
 
 /**
@@ -945,10 +920,15 @@ static inline int device_pm_get_sync(const struct device *dev) { return -ENOTSUP
 static inline int device_pm_put(const struct device *dev) { return -ENOTSUP; }
 static inline int device_pm_put_sync(const struct device *dev) { return -ENOTSUP; }
 #endif
-#else
-#define device_pm_control_nop(...) NULL
 #endif
 
+/**
+ * @brief Alias for legacy use of device_pm_control_nop.
+ *
+ * @note Usage of NULL is preferred, this alias will eventually be removed.
+ */
+#define device_pm_control_nop NULL
+
 /**
  * @}
  */

kernel/device.c

@@ -193,15 +193,6 @@ int device_required_foreach(const struct device *dev,
 }
 
 #ifdef CONFIG_PM_DEVICE
-int device_pm_control_nop(const struct device *unused_device,
-			  uint32_t unused_ctrl_command,
-			  void *unused_context,
-			  device_pm_cb cb,
-			  void *unused_arg)
-{
-	return -ENOTSUP;
-}
-
 int device_any_busy_check(void)
 {
 	const struct device *dev = __device_start;

subsys/power/device.c

@@ -142,8 +142,7 @@ void pm_create_device_list(void)
 		const struct device *dev = &all_devices[pmi];
 
 		/* Ignore "device"s that don't support PM */
-		if ((dev->device_pm_control == NULL) ||
+		if (dev->device_pm_control == NULL) {
-		    (dev->device_pm_control == device_pm_control_nop)) {
 			continue;
 		}