drivers: serial: add pin inversion to stm32 u(s)art

Additional properties are added to stm32 u(s)art to allow
for signal inversion.

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

drivers/serial/uart_stm32.c

@@ -1639,6 +1639,18 @@ static int uart_stm32_init(const struct device *dev)
 	}
 #endif
 
+#ifdef LL_USART_RXPIN_LEVEL_INVERTED
+	if (config->rx_invert) {
+		LL_USART_SetRXPinLevel(config->usart, LL_USART_RXPIN_LEVEL_INVERTED);
+	}
+#endif
+
+#ifdef LL_USART_TXPIN_LEVEL_INVERTED
+	if (config->tx_invert) {
+		LL_USART_SetTXPinLevel(config->usart, LL_USART_TXPIN_LEVEL_INVERTED);
+	}
+#endif
+
 	LL_USART_Enable(config->usart);
 
 #ifdef USART_ISR_TEACK
@@ -1751,6 +1763,8 @@ static const struct uart_stm32_config uart_stm32_cfg_##index = {	\
 	.pcfg = PINCTRL_DT_INST_DEV_CONFIG_GET(index),			\
 	.single_wire = DT_INST_PROP_OR(index, single_wire, false),	\
 	.tx_rx_swap = DT_INST_PROP_OR(index, tx_rx_swap, false),	\
+	.rx_invert = DT_INST_PROP(index, rx_invert),	\
+	.tx_invert = DT_INST_PROP(index, tx_invert),	\
 	STM32_UART_IRQ_HANDLER_FUNC(index)				\
 };									\
 									\

drivers/serial/uart_stm32.h

@@ -32,6 +32,10 @@ struct uart_stm32_config {
 	bool single_wire;
 	/* enable tx/rx pin swap */
 	bool tx_rx_swap;
+	/* enable rx pin inversion */
+	bool rx_invert;
+	/* enable tx pin inversion */
+	bool tx_invert;
 	const struct pinctrl_dev_config *pcfg;
 #if defined(CONFIG_UART_INTERRUPT_DRIVEN) || defined(CONFIG_UART_ASYNC_API) || \
 	defined(CONFIG_PM)

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

@@ -14,6 +14,20 @@ properties:
     clocks:
       required: true
 
+    tx-invert:
+      type: boolean
+      required: false
+      description: |
+        Invert the binary logic of tx pin. When enabled, physical logic levels are inverted and
+        we use 1=Low, 0=High instead of 1=High, 0=Low.
+
+    rx-invert:
+      type: boolean
+      required: false
+      description: |
+        Invert the binary logic of rx pin. When enabled, physical logic levels are inverted and
+        we use 1=Low, 0=High instead of 1=High, 0=Low.
+
     pinctrl-0:
       required: true
 

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

@@ -20,6 +20,20 @@ properties:
         only TX pin is used afterwards and should be configured.
         RX/TX conflicts must be handled on user side.
 
+    tx-invert:
+      type: boolean
+      required: false
+      description: |
+        Invert the binary logic of tx pin. When enabled, physical logic levels are inverted and
+        we use 1=Low, 0=High instead of 1=High, 0=Low.
+
+    rx-invert:
+      type: boolean
+      required: false
+      description: |
+        Invert the binary logic of rx pin. When enabled, physical logic levels are inverted and
+        we use 1=Low, 0=High instead of 1=High, 0=Low.
+
     pinctrl-0:
       required: true
 

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

@@ -26,6 +26,20 @@ properties:
       description: |
         Swap the TX and RX pins. Used in case of a cross-wired connection.
 
+    tx-invert:
+      type: boolean
+      required: false
+      description: |
+        Invert the binary logic of tx pin. When enabled, physical logic levels are inverted and
+        we use 1=Low, 0=High instead of 1=High, 0=Low.
+
+    rx-invert:
+      type: boolean
+      required: false
+      description: |
+        Invert the binary logic of rx pin. When enabled, physical logic levels are inverted and
+        we use 1=Low, 0=High instead of 1=High, 0=Low.
+
     pinctrl-0:
       required: true