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The USB core will currently fail to detect disconnections if a new device has attached by the time the port is examined in usb_hotplug(). Fix by recording the fact that a disconnection has taken place whenever the "connection status changed" (CSC) bit is observed to be set. (Whether the change represents a disconnection or a reconnection, it indicates that the port has experienced some time of being disconnected.) Note that the time at which a disconnection can be detected varies by hub type. In particular: root hubs can observe the CSC bit when polling, and so will record the disconnection before calling usb_port_changed(), but USB hubs read the port status (and hence the CSC bit) only during the call to hub_speed(), long after the call to usb_port_changed(). Signed-off-by: Michael Brown <mcb30@ipxe.org>