On Tue, Apr 03, 2012 at 03:24:18PM -0400, Alan Stern wrote:
> This patch (as1533) fixes a race between root-hub suspend and remote
> wakeup. If a wakeup event occurs while a root hub is suspending, it
> might not cause the suspend to fail. Although the host controller
> drivers check for pending wakeup events at the start of their
> bus_suspend routines, they generally do not check for wakeup events
> while the routines are running.
>
> In addition, if a wakeup event occurs any time after khubd is frozen
> and before the root hub is fully suspended, it might not cause a
> system sleep transition to fail. For example, the host controller
> drivers do not fail root-hub suspends when a connect-change event is
> pending.
>
> To fix both these issues, this patch causes hcd_bus_suspend() to query
> the controller driver's hub_status_data method after a root hub is
> suspended, if the root hub is enabled for wakeup. Any pending status
> changes will count as wakeup events, causing the root hub to be
> resumed and the overall suspend to fail with -EBUSY.
>
> A significant point is that not all events are reflected immediately
> in the status bits. Both EHCI and UHCI controllers notify the CPU
> when remote wakeup begins on a port, but the port's suspend-change
> status bit doesn't get set until after the port has completed the
> transition out of the suspend state, some 25 milliseconds later.
> Consequently, the patch will interpret any nonzero return value from
> hub_status_data as indicating a pending event, even if none of the
> status bits are set in the data buffer. Follow-up patches make the
> necessary changes to ehci-hcd and uhci-hcd.
>
> Signed-off-by: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>
> CC: Sarah Sharp <sarah.a.sharp@xxxxxxxxxxxxxxx>
> CC: Chen Peter-B29397 <B29397@xxxxxxxxxxxxx>
> CC: <stable@xxxxxxxxxxxxxxx>
>
> ---
>
> drivers/usb/core/hcd.c | 12 ++++++++++++
> 1 file changed, 12 insertions(+)
>
> Index: usb-3.3/drivers/usb/core/hcd.c
> ===================================================================
> --- usb-3.3.orig/drivers/usb/core/hcd.c
> +++ usb-3.3/drivers/usb/core/hcd.c
> @@ -1978,6 +1978,18 @@ int hcd_bus_suspend(struct usb_device *r
> if (status == 0) {
> usb_set_device_state(rhdev, USB_STATE_SUSPENDED);
> hcd->state = HC_STATE_SUSPENDED;
> +
> + /* Did we race with a root-hub wakeup event? */
> + if (rhdev->do_remote_wakeup) {
> + char buffer[6];
> +
> + status = hcd->driver->hub_status_data(hcd, buffer);
I have run this patch at FSL board, and found the kernel is hang at reading
portsc of above code, the reason is controller is off after bus suspend. I
have checked the ehci-tegra.c, it also powers off its controller at bus
suspend, maybe there are other controllers also do that.
> + if (status != 0) {
> + dev_dbg(&rhdev->dev, "suspend raced with wakeup event\n");
> + hcd_bus_resume(rhdev, PMSG_AUTO_RESUME);
> + status = -EBUSY;
> + }
> + }
> } else {
> spin_lock_irq(&hcd_root_hub_lock);
> if (!HCD_DEAD(hcd)) {
>
>
--
Best Regards,
Peter Chen
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