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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)) {
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