serial: max310x: turn off transmitter before activating AutoCTS or auto transmitter flow control

As documented in the data-sheet, the transmitter must be disabled before
activating AutoCTS or auto transmitter flow control. Accordingly, the
transmitter must be enabled after AutoCTS or auto transmitter flow
control gets deactivated.

Signed-off-by: Christoph Vogtländer <c.vogtlaender@sigma-surface-science.com>
Link: https://lore.kernel.org/r/20190904121746.4641-1-c.vogtlaender@sigma-surface-science.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 18 insertions, 0 deletions

diff --git a/drivers/tty/serial/max310x.c b/drivers/tty/serial/max310x.c
index aed19c688beb..8434bd5a8ec7 100644
--- a/drivers/tty/serial/max310x.c
+++ b/drivers/tty/serial/max310x.c
@@ -956,6 +956,15 @@ static void max310x_set_termios(struct uart_port *port,
         max310x_port_write(port, MAX310X_XON1_REG, termios->c_cc[VSTART]);
         max310x_port_write(port, MAX310X_XOFF1_REG, termios->c_cc[VSTOP]);
 
+        /* Disable transmitter before enabling AutoCTS or auto transmitter
+         * flow control
+         */
+        if (termios->c_cflag & CRTSCTS || termios->c_iflag & IXOFF) {
+                max310x_port_update(port, MAX310X_MODE1_REG,
+                                    MAX310X_MODE1_TXDIS_BIT,
+                                    MAX310X_MODE1_TXDIS_BIT);
+        }
+
         port->status &= ~(UPSTAT_AUTOCTS | UPSTAT_AUTORTS | UPSTAT_AUTOXOFF);
 
         if (termios->c_cflag & CRTSCTS) {
@@ -974,6 +983,15 @@ static void max310x_set_termios(struct uart_port *port,
         }
         max310x_port_write(port, MAX310X_FLOWCTRL_REG, flow);
 
+        /* Enable transmitter after disabling AutoCTS and auto transmitter
+         * flow control
+         */
+        if (!(termios->c_cflag & CRTSCTS) && !(termios->c_iflag & IXOFF)) {
+                max310x_port_update(port, MAX310X_MODE1_REG,
+                                    MAX310X_MODE1_TXDIS_BIT,
+                                    0);
+        }
+
         /* Get baud rate generator configuration */
         baud = uart_get_baud_rate(port, termios, old,
                                   port->uartclk / 16 / 0xffff,