drivers: uart: Add support for st single wire mode

An additional devicetree poperty `single-wire` is added
to uart and usart bindings of stm32. The driver checks this value
during initialization and enables the single wire mode when set.

Signed-off-by: Jonathan Hahn <Jonathan.Hahn@t-online.de>

drivers/serial/uart_stm32.c

@@ -1585,6 +1585,11 @@ static int uart_stm32_init(const struct device *dev)
 	/* Set the default baudrate */
 	uart_stm32_set_baudrate(dev, data->baud_rate);
 
+	/* Enable the single wire / half-duplex mode */
+	if (config->single_wire) {
+		LL_USART_EnableHalfDuplex(UartInstance);
+	}
+
 	LL_USART_Enable(UartInstance);
 
 #ifdef USART_ISR_TEACK
@@ -1701,6 +1706,7 @@ static const struct uart_stm32_config uart_stm32_cfg_##index = {	\
 	.hw_flow_control = DT_INST_PROP(index, hw_flow_control),	\
 	.parity = DT_INST_ENUM_IDX_OR(index, parity, UART_CFG_PARITY_NONE),	\
 	.pcfg = PINCTRL_DT_INST_DEV_CONFIG_GET(index),			\
+	.single_wire = DT_INST_PROP_OR(index, single_wire, false), \
 	STM32_UART_POLL_IRQ_HANDLER_FUNC(index)				\
 };									\
 									\

drivers/serial/uart_stm32.h

@@ -23,6 +23,8 @@ struct uart_stm32_config {
 	bool hw_flow_control;
 	/* initial parity, 0 for none, 1 for odd, 2 for even */
 	int  parity;
+	/* switch to enable single wire / half duplex feature */
+	bool single_wire;
 	const struct pinctrl_dev_config *pcfg;
 #if defined(CONFIG_PM) \
 	&& !defined(CONFIG_UART_INTERRUPT_DRIVEN) \

dts/bindings/serial/st,stm32-uart.yaml

@@ -11,6 +11,15 @@ properties:
     interrupts:
       required: true
 
+    single-wire:
+      type: boolean
+      required: false
+      description: |
+        Enable the single wire half-duplex communication.
+        Using this mode, TX and RX lines are internally connected and
+        only TX pin is used afterwards and should be configured.
+        RX/TX conflicts must be handled on user side.
+
     pinctrl-0:
       required: true
 

dts/bindings/serial/st,stm32-usart.yaml

@@ -11,6 +11,15 @@ properties:
     interrupts:
       required: true
 
+    single-wire:
+      type: boolean
+      required: false
+      description: |
+        Enable the single wire half-duplex communication.
+        Using this mode, TX and RX lines are internally connected and
+        only TX pin is used afterwards and should be configured.
+        RX/TX conflicts must be handled on user side.
+
     pinctrl-0:
       required: true