On Wed, 21 Nov 2012, Sarah Sharp wrote: > The USB core disables the USB 2.0 ports in several different error > cases. It expects that all USB hubs will act like external hubs, and > always return an interrupt event if a port change bit is set. External > USB 2.0 and USB 3.0 hubs are level-triggered, so this works for them. > > However, xHCI roothubs are edge-triggered. If no port status change > bits are set, and a new change bit is set, the xHCI host sends an > interrupt and a Port Status Change Event. It will not generate another > port event until all change bits are cleared and a new one is set. > > This opens up issues with the USB core port disabling code. Right now, > it assumes that it can simply clear the port enable bit, and wait for > the hub to send an interrupt when a change bit is set. If previous > change bits weren't cleared, it's assumed to be fine because the hub > will continue to remind the USB core about them through the interrupt > endpoint. Is port-disabling the only place where this problem occurs? A more defensive approach would be to copy what ohci-hcd does. When a port-change interrupt occurs, the driver switches over to polling for root-hub status changes. It doesn't switch back to interrupt-driven operation until the hub_status_data routine sees that none of the ports have any change bits set. > diff --git a/drivers/usb/host/xhci-hub.c b/drivers/usb/host/xhci-hub.c > index a686cf4..7d9dcd6 100644 > --- a/drivers/usb/host/xhci-hub.c > +++ b/drivers/usb/host/xhci-hub.c > @@ -340,6 +340,10 @@ static void xhci_disable_port(struct usb_hcd *hcd, struct xhci_hcd *xhci, > return; > } > > + /* Clear all change bits, so that we get a device connect event. */ > + port_status |= PORT_CSC | PORT_PEC | PORT_WRC | > + PORT_OCC | PORT_RC | PORT_PLC | > + PORT_CEC; What if a connect-change occurred just before this? Would it get lost? Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
