drivers: uart: stm32: Complete wakeup feature

Serial wakeup feature was only working whe DBG in Stop mode setting
was enabled.
Add required changes to make it functional also when this configuration
isn't set.

Signed-off-by: Erwan Gouriou <[email protected]>

Author: erwango

drivers/serial/uart_stm32.c

@@ -1278,6 +1278,18 @@ static void uart_stm32_isr(const struct device *dev)
 	/* Clear errors */
 	uart_stm32_err_check(dev);
 #endif /* CONFIG_UART_ASYNC_API */
+
+#ifdef CONFIG_PM
+	if (LL_USART_IsEnabledIT_WKUP(config->usart) &&
+		LL_USART_IsActiveFlag_WKUP(config->usart)) {
+
+		LL_USART_ClearFlag_WKUP(config->usart);
+#ifdef USART_ISR_REACK
+		while (LL_USART_IsActiveFlag_REACK(config->usart) == 0) {
+		}
+#endif
+	}
+#endif
 }
 #endif /* CONFIG_UART_INTERRUPT_DRIVEN || CONFIG_UART_ASYNC_API || CONFIG_PM */
 
@@ -2005,7 +2017,14 @@ static int uart_stm32_init(const struct device *dev)
 		 * CONFIG_PM_DEVICE=n : Always active
 		 * CONFIG_PM_DEVICE=y : Controlled by pm_device_wakeup_enable()
 		 */
+
+		LL_USART_Disable(config->usart);
+		LL_USART_SetWKUPType(config->usart, LL_USART_WAKEUP_ON_RXNE);
+		LL_USART_EnableIT_WKUP(config->usart);
+		LL_USART_ClearFlag_WKUP(config->usart);
 		LL_USART_EnableInStopMode(config->usart);
+		LL_USART_Enable(config->usart);
+
 		if (config->wakeup_line != STM32_EXTI_LINE_NONE) {
 			/* Prepare the WAKEUP with the expected EXTI line */
 			LL_EXTI_EnableIT_0_31(BIT(config->wakeup_line));