The USART can act either as a LIN master node or as a LIN slave node.
The node configuration is chosen by setting USART_MR.USART_MODE:
In order to avoid unpredictable behavior, any change of the LIN node configuration must be followed by a software reset of the transmitter and of the receiver (except the initial node configuration after a hardware reset). (See “Receiver and Transmitter Control”.)