[PATCH] Serial: Check status of CTS when using flow control

Fix bugme #4712: read the CTS status and set hw_stopped if CTS
is not active when opening the port and/or enabling CRTSCTS

Thanks to Stefan Wolff for spotting this problem.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

1 files changed, 17 insertions, 0 deletions

diff --git a/drivers/serial/serial_core.c b/drivers/serial/serial_core.c
index f5ce58d0514d..139863a787f3 100644
--- a/drivers/serial/serial_core.c
+++ b/drivers/serial/serial_core.c
@@ -182,6 +182,13 @@ static int uart_startup(struct uart_state *state, int init_hw)
                                 uart_set_mctrl(port, TIOCM_RTS | TIOCM_DTR);
                 }
 
+                if (info->flags & UIF_CTS_FLOW) {
+                        spin_lock_irq(&port->lock);
+                        if (!(port->ops->get_mctrl(port) & TIOCM_CTS))
+                                info->tty->hw_stopped = 1;
+                        spin_unlock_irq(&port->lock);
+                }
+
                 info->flags |= UIF_INITIALIZED;
 
                 clear_bit(TTY_IO_ERROR, &info->tty->flags);
@@ -1134,6 +1141,16 @@ static void uart_set_termios(struct tty_struct *tty, struct termios *old_termios
                 spin_unlock_irqrestore(&state->port->lock, flags);
         }
 
+        /* Handle turning on CRTSCTS */
+        if (!(old_termios->c_cflag & CRTSCTS) && (cflag & CRTSCTS)) {
+                spin_lock_irqsave(&state->port->lock, flags);
+                if (!(state->port->ops->get_mctrl(state->port) & TIOCM_CTS)) {
+                        tty->hw_stopped = 1;
+                        state->port->ops->stop_tx(state->port, 0);
+                }
+                spin_unlock_irqrestore(&state->port->lock, flags);
+        }
+
 #if 0
         /*
          * No need to wake up processes in open wait, since they