[BACKPORT] RCInput:Add Support for RX-TX SWAP using onewire

A board can optionaly define RC_SERIAL_SWAP_USING_SINGLEWIRE
   If the board is wired board with TX to the input (Swapped) and
   the SoC does not support U[S]ART level RX-TX swapping to allow
   useing onewire to do the swap if and only if:

     RC_SERIAL_SWAP_USING_SINGLEWIRE   is defined
     RC_SERIAL_SWAP_RXTX               is defined
     TIOCSSWAP                         is defined and retuns !OK
     TIOCSSINGLEWIRE                   is defined

platforms/common/include/px4_platform_common/board_common.h

@@ -465,6 +465,15 @@ static inline bool board_rc_singlewire(const char *device) { return false; }
  *   A board may define RC_SERIAL_SWAP_RXTX, so that RC_SERIAL_PORT is configured
  *   as UART with RX/TX swapped.
  *
+ *   It can optionaly define RC_SERIAL_SWAP_USING_SINGLEWIRE If the board is wired
+ *   with TX to the input (Swapped) and the SoC does not support U[S]ART level
+ *   HW swapping, then use onewire to do the swap if and only if:
+ *
+ *    RC_SERIAL_SWAP_USING_SINGLEWIRE   is defined
+ *    RC_SERIAL_SWAP_RXTX               is defined
+ *    TIOCSSWAP                         is defined and retuns !OK
+ *    TIOCSSINGLEWIRE                   is defined
+ *
  * Input Parameters:
  *   device: serial device, e.g. "/dev/ttyS0"
  *

src/drivers/rc_input/RCInput.cpp

@@ -296,6 +296,25 @@ void RCInput::rc_io_invert(bool invert)
 	}
 }
 
+void  RCInput::swap_rx_tx()
+{
+#if defined(RC_SERIAL_SWAP_USING_SINGLEWIRE)
+	int rv = -ENOTTY;
+#  if defined(TIOCSSWAP)
+	rv = ioctl(_rcs_fd, TIOCSSWAP, SER_SWAP_ENABLED);
+#  endif // TIOCSSWAP
+#  ifdef TIOCSSINGLEWIRE
+
+	if (rv != OK) {
+		ioctl(_rcs_fd, TIOCSSINGLEWIRE, SER_SINGLEWIRE_ENABLED);
+	}
+
+#  else
+	UNUSED(rv);
+#  endif // TIOCSSINGLEWIRE
+#endif // RC_SERIAL_SWAP_USING_SINGLEWIRE
+}
+
 void RCInput::Run()
 {
 	if (should_exit()) {
@@ -488,6 +507,7 @@ void RCInput::Run()
 				_rc_scan_begin = cycle_timestamp;
 				// Configure serial port for DSM
 				dsm_config(_rcs_fd);
+				swap_rx_tx();
 
 				// flush serial buffer and any existing buffered data
 				tcflush(_rcs_fd, TCIOFLUSH);
@@ -525,6 +545,7 @@ void RCInput::Run()
 				_rc_scan_begin = cycle_timestamp;
 				// Configure serial port for DSM
 				dsm_config(_rcs_fd);
+				swap_rx_tx();
 
 				// flush serial buffer and any existing buffered data
 				tcflush(_rcs_fd, TCIOFLUSH);
@@ -576,6 +597,7 @@ void RCInput::Run()
 				_rc_scan_begin = cycle_timestamp;
 				// Configure serial port for DSM
 				dsm_config(_rcs_fd);
+				swap_rx_tx();
 
 				// flush serial buffer and any existing buffered data
 				tcflush(_rcs_fd, TCIOFLUSH);
@@ -654,6 +676,7 @@ void RCInput::Run()
 				_rc_scan_begin = cycle_timestamp;
 				// Configure serial port for CRSF
 				crsf_config(_rcs_fd);
+				swap_rx_tx();
 
 				// flush serial buffer and any existing buffered data
 				tcflush(_rcs_fd, TCIOFLUSH);
@@ -702,6 +725,7 @@ void RCInput::Run()
 				_rc_scan_begin = cycle_timestamp;
 				// Configure serial port for GHST
 				ghst_config(_rcs_fd);
+				swap_rx_tx();
 
 				// flush serial buffer and any existing buffered data
 				tcflush(_rcs_fd, TCIOFLUSH);

src/drivers/rc_input/RCInput.hpp

@@ -126,6 +126,7 @@ private:
 	void set_rc_scan_state(RC_SCAN _rc_scan_state);
 
 	void rc_io_invert(bool invert);
+	void swap_rx_tx(void);
 
 	hrt_abstime _rc_scan_begin{0};