[usb] Detect missed disconnections

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>

1 files changed, 12 insertions, 10 deletions

diff --git a/src/drivers/bus/usb.c b/src/drivers/bus/usb.c
index 2191867a..2b9efa45 100644
--- a/src/drivers/bus/usb.c
+++ b/src/drivers/bus/usb.c
@@ -1589,18 +1589,20 @@ static int usb_hotplug ( struct usb_port *port ) {
 		return rc;
 	}
 
-	/* Handle attached/detached device as applicable */
-	if ( port->speed && ! port->attached ) {
-		/* Newly attached device */
-		return usb_attached ( port );
-	} else if ( port->attached && ! port->speed ) {
-		/* Newly detached device */
+	/* Detach device, if applicable */
+	if ( port->attached && ( port->disconnected || ! port->speed ) )
 		usb_detached ( port );
-		return 0;
-	} else {
-		/* Ignore */
-		return 0;
+
+	/* Attach device, if applicable */
+	if ( port->speed && ! port->attached ) {
+		if ( ( rc = usb_attached ( port ) ) != 0 )
+			return rc;
 	}
+
+	/* Clear any recorded disconnections */
+	port->disconnected = 0;
+
+	return 0;
 }
 
 /******************************************************************************