This patch allows RS485 Half Duplex (ATMEL_US_USMODE_RS485 is half duplex) to
work even if handshaking is turned on.  This mimics the behavior of the EXAR
USB/Serial driver known as Vizzini.  It is impossible to use handshaking when
using ATMEL_US_USMODE_RS485.  This provides compatibility between MTCDT-0.1 and
MTCDT-0.2.
=======================================================================================
diff -Naru orig/drivers/tty/serial/atmel_serial.c new/drivers/tty/serial/atmel_serial.c
--- orig/drivers/tty/serial/atmel_serial.c	2021-11-29 12:29:38.472076748 -0600
+++ new/drivers/tty/serial/atmel_serial.c	2021-11-29 12:26:05.668072459 -0600
@@ -2171,7 +2171,10 @@
 		atmel_uart_writel(port, ATMEL_US_TTGR,
 				  port->rs485.delay_rts_after_send);
 		mode |= ATMEL_US_USMODE_RS485;
+		/* CRTSCTS is impossible in RS485 mode, and breaks the driver
+		 * so we cannot do a send. */
+		termios->c_cflag &= ~CRTSCTS;
 	} else if (termios->c_cflag & CRTSCTS) {
 		/* RS232 with hardware handshake (RTS/CTS) */
 		if (atmel_use_fifo(port) &&
 		    !mctrl_gpio_to_gpiod(atmel_port->gpios, UART_GPIO_CTS)) {