drivers: serial: Reset UART using RCC before initialization

In multi-image environment, after jump to the image we can have UART in
unexpected state. Reset UART to default state to make sure that UART is
initialized properly and won't cause system to crash or hang.

Signed-off-by: Patryk Duda <pdk@semihalf.com>

drivers/serial/Kconfig.stm32

@@ -16,6 +16,7 @@ config UART_STM32
 		   DT_HAS_ST_STM32_DMA_V2BIS_ENABLED || \
 		   DT_HAS_ST_STM32U5_DMA_ENABLED
 	select DMA if UART_ASYNC_API
+	select RESET
 	help
 	  This option enables the UART driver for STM32 family of
 	  processors.

drivers/serial/uart_stm32.c

@@ -21,6 +21,7 @@
 #include <zephyr/init.h>
 #include <zephyr/drivers/uart.h>
 #include <zephyr/drivers/clock_control.h>
+#include <zephyr/drivers/reset.h>
 #include <zephyr/pm/policy.h>
 #include <zephyr/pm/device.h>
 
@@ -1620,6 +1621,14 @@ static int uart_stm32_init(const struct device *dev)
 
 	LL_USART_Disable(config->usart);
 
+	if (!device_is_ready(data->reset.dev)) {
+		LOG_ERR("reset controller not ready");
+		return -ENODEV;
+	}
+
+	/* Reset UART to default state using RCC */
+	reset_line_toggle_dt(&data->reset);
+
 	/* TX/RX direction */
 	LL_USART_SetTransferDirection(config->usart,
 				      LL_USART_DIRECTION_TX_RX);
@@ -1896,6 +1905,7 @@ static const struct uart_stm32_config uart_stm32_cfg_##index = {	\
 									\
 static struct uart_stm32_data uart_stm32_data_##index = {		\
 	.baud_rate = DT_INST_PROP(index, current_speed),		\
+	.reset = RESET_DT_SPEC_GET(DT_DRV_INST(index)),			\
 	UART_DMA_CHANNEL(index, rx, RX, PERIPHERAL, MEMORY)		\
 	UART_DMA_CHANNEL(index, tx, TX, MEMORY, PERIPHERAL)		\
 };									\

drivers/serial/uart_stm32.h

@@ -76,6 +76,8 @@ struct uart_stm32_data {
 	uint32_t baud_rate;
 	/* clock device */
 	const struct device *clock;
+	/* Reset controller device configuration */
+	const struct reset_dt_spec reset;
 #ifdef CONFIG_UART_INTERRUPT_DRIVEN
 	uart_irq_callback_user_data_t user_cb;
 	void *user_data;