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    USB: fix race between root-hub suspend and remote wakeup · 879d38e6
    Alan Stern 提交于
    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: NAlan Stern <stern@rowland.harvard.edu>
    CC: Sarah Sharp <sarah.a.sharp@linux.intel.com>
    CC: Chen Peter-B29397 <B29397@freescale.com>
    Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
    879d38e6
hcd.c 76.6 KB