• Ming Lei's avatar
    USB: EHCI: improve interrupt qh unlink · 9118f9eb
    Ming Lei authored
    ehci-hcd currently unlinks an interrupt QH when it becomes empty, that
    is, after its last URB completes.  This works well because in almost
    all cases, the completion handler for an interrupt URB resubmits the
    URB; therefore the QH doesn't become empty and doesn't get unlinked.
    
    When we start using tasklets for URB completion, this scheme won't work
    as well.  The resubmission won't occur until the tasklet runs, which
    will be some time after the completion is queued with the tasklet.
    During that delay, the QH will be empty and so will be unlinked
    unnecessarily.
    
    To prevent this problem, this patch adds a 5-ms time delay before empty
    interrupt QHs are unlinked.  Most often, during that time the interrupt
    URB will be resubmitted and thus we can avoid unlinking the QH.
    Signed-off-by: default avatarAlan Stern <stern@rowland.harvard.edu>
    Signed-off-by: default avatarMing Lei <ming.lei@canonical.com>
    Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
    9118f9eb
ehci.h 25.7 KB