tty_prepare_flip_string
count = tty_prepare_flip_string(&qtty->port, &buf, count);
len = tty_prepare_flip_string(&port->port, &dst,
len = tty_prepare_flip_string(&port->port, &dst,
EXPORT_SYMBOL_GPL(tty_prepare_flip_string);
size_t tty_prepare_flip_string(struct tty_port *port, u8 **chars, size_t size);