On 04/04/2012 03:24 AM, Alan Stern wrote: > Greg: > > The following series of patches fixes an outstanding race between > suspending a root hub and getting a wakeup event on any of the root > hub's ports. > > Currently we don't handle these races very well. The host controller > drivers check for some wakeup events before starting a suspend but not > for all (e.g., they check for port resume in progress but not port > connect change). Also, the drivers don't check for wakeup events that > occur while the root hub is being suspended, or events that occurred > before the suspend began but have not yet been handled. > > The first patch fixes the general problem by making > usb_hcd_bus_suspend() query each HCD's hub_status_data method after > suspending its root hub, if that root hub is enabled for wakeup. A > nonzero return value, indicating that a status change is pending, will > cause the root hub to be resumed and the suspend attempt to fail with > -EBUSY. > > The second and third patches make some necessary adjustments to > ehci-hcd and uhci-hcd. Right now the hub_status_data methods return a > nonzero value only when some of the status bits are set. However, in > the case of a remote wakeup request received from downstream, the > port's suspend-change status bit doesn't get set until _after_ the port > resume is complete, which is at least 25 ms after the CPU is notified > about the wakeup request. The patches make the hub_status_data methods > return nonzero while the port resume is in progress, even if none of > the status bits are set. > > Although I'm not familiar with the details of xhci-hcd's root-hub > management, I assume that it will need adjustments quite similar to > those for ehci-hcd. Sarah, please take note. For the most part, you > or Andiry ought to be able to copy the changes I made -- they are > pretty simple. > I've created the corresponding patch for xHCI, most codes and the description are copied from your patch for ehci-hcd. Seems remote wakeup works fine, but I don't know how to trigger the race case. So I sent it out as RFC. Thanks, Andiry -- 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
