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    Subject[ 003/127] USB: fix latency in uhci-hcd and ohci-hcd
    Date
    3.9-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Alan Stern <stern@rowland.harvard.edu>

    commit e1944017839d7dfbf7329fac4bdec8b4050edf5e upstream.

    Commits c44b225077bb1fb25ed5cd5c4f226897b91bedd4 (UHCI: implement new
    semantics for URB_ISO_ASAP) and
    6a41b4d3fe8cd4cc95181516fc6fba7b1747a27c (OHCI: implement new
    semantics for URB_ISO_ASAP) increased the latency for isochronous URBs
    in uhci-hcd and ohci-hcd respectively to 2 milliseconds, in an
    attempt to avoid underruns. It turns out that not only was this
    unnecessary -- 1-ms latency works okay -- it also causes problems with
    certain application loads such as real-time audio.

    This patch changes the latency for both drivers back to 1 ms.

    This should be applied to -stable kernels going back to 3.8.

    Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
    Reported-and-tested-by: Joe Rayhawk <jrayhawk@fairlystable.org>
    CC: Clemens Ladisch <clemens@ladisch.de>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    drivers/usb/host/ohci-hcd.c | 2 +-
    drivers/usb/host/uhci-q.c | 2 +-
    2 files changed, 2 insertions(+), 2 deletions(-)

    --- a/drivers/usb/host/ohci-hcd.c
    +++ b/drivers/usb/host/ohci-hcd.c
    @@ -233,7 +233,7 @@ static int ohci_urb_enqueue (
    urb->start_frame = frame;
    }
    } else if (ed->type == PIPE_ISOCHRONOUS) {
    - u16 next = ohci_frame_no(ohci) + 2;
    + u16 next = ohci_frame_no(ohci) + 1;
    u16 frame = ed->last_iso + ed->interval;

    /* Behind the scheduling threshold? */
    --- a/drivers/usb/host/uhci-q.c
    +++ b/drivers/usb/host/uhci-q.c
    @@ -1287,7 +1287,7 @@ static int uhci_submit_isochronous(struc
    return -EINVAL; /* Can't change the period */

    } else {
    - next = uhci->frame_number + 2;
    + next = uhci->frame_number + 1;

    /* Find the next unused frame */
    if (list_empty(&qh->queue)) {



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