USB: fix EHCI periodic transfers
As noted by Stefan Neis <Stefan.Neis@kobil.com>, we had a recent regression with EHCI periodic transfers, in some (seemingly not all that common) cases. The root cause was that the schedule activation was only loosely coupled to the addition or removal of transfers, so two different execution contexts could both think they had to deactivate (or conversely activate) the schedule. So this fix tightens that coupling, managing it more like a refcount. Signed-off-by: NDavid Brownell <dbrownell@users.sourceforge.net> Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>
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