tty: Implement a drain delay in the tty port

We need this for devices that cannot flush and wait, but which do not order
data and modem events. Without it we will hang up before all the data
clears the hardware. Needed for the USB changes.
Signed-off-by: NAlan Cox <alan@linux.intel.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

drivers/char/tty_port.c

@@ -308,6 +308,17 @@ int tty_port_close_start(struct tty_port *port, struct tty_struct *tty, struct f
 	if (port->flags & ASYNC_INITIALIZED &&
 			port->closing_wait != ASYNC_CLOSING_WAIT_NONE)
 		tty_wait_until_sent(tty, port->closing_wait);
+	if (port->drain_delay) {
+		unsigned int bps = tty_get_baud_rate(tty);
+		long timeout;
+
+		if (bps > 1200)
+			timeout = max_t(long, (HZ * 10 * port->drain_delay) / bps,
+								HZ / 10);
+		else
+			timeout = 2 * HZ;
+		schedule_timeout_interruptible(timeout);
+	}
 	return 1;
 }
 EXPORT_SYMBOL(tty_port_close_start);

include/linux/tty.h

@@ -201,6 +201,9 @@ struct tty_port {
 	unsigned char		*xmit_buf;	/* Optional buffer */
 	int			close_delay;	/* Close port delay */
 	int			closing_wait;	/* Delay for output */
+	int			drain_delay;	/* Set to zero if no pure time
+						   based drain is needed else
+						   set to size of fifo */
 };
 
 /*