driver: uart: npcx: Add pm_deivce support for uart driver.

Since the uart device clock will be stopped after ec entered sleep or
deep sleep state and restore its clock automatically, there is no need
to implement code for suspending and resuming devices manually.

The driver still needs to check the current status of uart device when
it wants to change its power state to LOW or SUSPEND power state. It is
crucial to forbid ec enters sleep or deep sleep state when uart device
is busy with transmitting data. Or we will observe broken characters on
the uart console.

Signed-off-by: Mulin Chao <mlchao@nuvoton.com>

drivers/serial/uart_npcx.c

@@ -11,6 +11,7 @@
 #include <drivers/uart.h>
 #include <drivers/clock_control.h>
 #include <kernel.h>
+#include <power/power.h>
 #include <soc.h>
 #include "soc_miwu.h"
 
@@ -37,6 +38,9 @@ struct uart_npcx_data {
 	uart_irq_callback_user_data_t user_cb;
 	void *user_data;
 #endif
+#ifdef CONFIG_PM_DEVICE
+	uint32_t pm_state;
+#endif
 };
 
 /* Driver convenience defines */
@@ -362,6 +366,72 @@ static int uart_npcx_init(const struct device *dev)
 	return 0;
 }
 
+#ifdef CONFIG_PM_DEVICE
+static inline bool uart_npcx_device_is_transmitting(const struct device *dev)
+{
+	if (IS_ENABLED(CONFIG_UART_INTERRUPT_DRIVEN)) {
+		/* The transmitted transaction is completed? */
+		return !uart_npcx_irq_tx_complete(dev);
+	}
+
+	/* No need for polling mode */
+	return 0;
+}
+
+static inline int uart_npcx_get_power_state(const struct device *dev,
+							uint32_t *state)
+{
+	const struct uart_npcx_data *const data = DRV_DATA(dev);
+
+	*state = data->pm_state;
+	return 0;
+}
+
+static inline int uart_npcx_set_power_state(const struct device *dev,
+							uint32_t next_state)
+{
+	struct uart_npcx_data *const data = DRV_DATA(dev);
+
+	/* If next device power state is LOW or SUSPEND power state */
+	if (next_state == DEVICE_PM_LOW_POWER_STATE ||
+	    next_state == DEVICE_PM_SUSPEND_STATE) {
+		/*
+		 * If uart device is busy with transmitting, the driver will
+		 * stay in while loop and wait for the transaction is completed.
+		 */
+		while (uart_npcx_device_is_transmitting(dev)) {
+			continue;
+		}
+	}
+
+	data->pm_state = next_state;
+	return 0;
+}
+
+/* Implements the device power management control functionality */
+static int uart_npcx_pm_control(const struct device *dev, uint32_t ctrl_command,
+				 void *context, device_pm_cb cb, void *arg)
+{
+	int ret = 0;
+
+	switch (ctrl_command) {
+	case DEVICE_PM_SET_POWER_STATE:
+		ret = uart_npcx_set_power_state(dev, *((uint32_t *)context));
+		break;
+	case DEVICE_PM_GET_POWER_STATE:
+		ret = uart_npcx_get_power_state(dev, (uint32_t *)context);
+		break;
+	default:
+		ret = -EINVAL;
+	}
+
+	if (cb != NULL) {
+		cb(dev, ret, context, arg);
+	}
+	return ret;
+}
+#endif /* CONFIG_PM_DEVICE */
+
 #ifdef CONFIG_UART_INTERRUPT_DRIVEN
 #define NPCX_UART_IRQ_CONFIG_FUNC_DECL(inst) \
 	static void uart_npcx_irq_config_##inst(const struct device *dev)
@@ -406,7 +476,7 @@ static int uart_npcx_init(const struct device *dev)
 									       \
 	DEVICE_DT_INST_DEFINE(inst,					       \
 			&uart_npcx_init,                                       \
-			device_pm_control_nop,				       \
+			uart_npcx_pm_control,				       \
 			&uart_npcx_data_##inst, &uart_npcx_cfg_##inst,         \
 			PRE_KERNEL_1, CONFIG_KERNEL_INIT_PRIORITY_DEVICE,      \
 			&uart_npcx_driver_api);                                \

soc/arm/nuvoton_npcx/npcx7/Kconfig.defconfig.series

@@ -97,9 +97,9 @@ config PM
 	  system enters idle state.
 
 config PM_DEVICE
-	default n
+	default y
 	help
-	  Disable device power management so far.
+	  Enable device power management support.
 
 endif # SOC_POWER_MANAGEMENT