[PATCH v2 2/2] usb: gadget serial: Honour termios CLOCAL on disconnect

["Kyösti Mälkki" <kyosti.malkki-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

There are applications where it is desirable to not hangup ttyGS* when
USB disconnect is detected. USB host side of communication may
power-cycle periodically or there may be the actual need to physically
disconnect and reconnect USB cable temporarily.

USB disconnects on serial gadget are comparable to loss of Carrier Detect
of conventional UARTs. With the change, if ttyGS* has termios CLOCAL flag
set, disconnect on USB does not hangup the TTY.

Signed-off-by: Kyösti Mälkki <kyosti.malkki-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
---
 drivers/usb/gadget/function/u_serial.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/usb/gadget/function/u_serial.c b/drivers/usb/gadget/function/u_serial.c
index 491082a..dabc165 100644
--- a/drivers/usb/gadget/function/u_serial.c
+++ b/drivers/usb/gadget/function/u_serial.c
@@ -1253,9 +1253,16 @@ void gserial_disconnect(struct gserial *gser)
 	port->port_usb = NULL;
 	gser->ioport = NULL;
 	if (port->port.count > 0 || port->openclose) {
+		struct tty_struct *tty;
+
 		wake_up_interruptible(&port->drain_wait);
-		if (port->port.tty)
-			tty_hangup(port->port.tty);
+		tty = port->port.tty;
+		if (tty) {
+			if (tty->termios.c_cflag & CLOCAL)
+				stop_tty(tty);
+			else
+				tty_hangup(tty);
+		}
 	}
 	spin_unlock_irqrestore(&port->port_lock, flags);
 
-- 
1.8.1.1

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