Original discussion:
http://thread.gmane.org/gmane.linux.usb.general/23217/focus=23248
or
http://marc.info/?l=linux-usb&m=125553790714133&w=2

The tty_port code inherited a bug common to various drivers it was based
upon. If the tty is opened O_NONBLOCK we do not wait for the carrier to be
raised but we must still raise our modem lines if appropriate.

(There is a second question here about whether we should do so if CLOCAL is
 set but that can wait)
Signed-off-by: Alan Cox <alan@linux.intel.com>
Reported-by: Karl Hiramoto <karl@hiramoto.org>
Tested-by: Karl Hiramoto <karl@hiramoto.org>
Cc: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>