tty: Sort out the USB sysrq changes that wrecked performance

We can't go around calling all sorts of magic per character functions at
full rate 3G data speed.
Signed-off-by: NAlan Cox <alan@linux.intel.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

drivers/usb/serial/generic.c

@@ -424,10 +424,17 @@ static void flush_and_resubmit_read_urb(struct usb_serial_port *port)
 	if (!tty)
 		goto done;
 
-	/* Push data to tty */
-	for (i = 0; i < urb->actual_length; i++, ch++) {
-		if (!usb_serial_handle_sysrq_char(port, *ch))
-			tty_insert_flip_char(tty, *ch, TTY_NORMAL);
+	/* The per character mucking around with sysrq path it too slow for
+	   stuff like 3G modems, so shortcircuit it in the 99.9999999% of cases
+	   where the USB serial is not a console anyway */
+	if (!port->console || !port->sysrq)
+		tty_insert_flip_string(tty, ch, urb->actual_length);
+	else {
+		/* Push data to tty */
+		for (i = 0; i < urb->actual_length; i++, ch++) {
+			if (!usb_serial_handle_sysrq_char(port, *ch))
+				tty_insert_flip_char(tty, *ch, TTY_NORMAL);
+		}
 	}
 	tty_flip_buffer_push(tty);
 	tty_kref_put(tty);