Add method, which waits until the transmission buffer has been sent.
Note, that the change in ttyport_write_wakeup is related, since
tty_wait_until_sent will hang without that change.
Acked-by: NRob Herring <robh@kernel.org>
Acked-by: NPavel Machek <pavel@ucw.cz>
Signed-off-by: NSebastian Reichel <sre@kernel.org>
Acked-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NMarcel Holtmann <marcel@holtmann.org>