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    Subject[ 179/221] xhci: Handle HS bulk/ctrl endpoints that dont NAK.
    Date
    3.7-stable review patch.  If anyone has any objections, please let me know.

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

    From: Sarah Sharp <sarah.a.sharp@linux.intel.com>

    commit 55c1945edaac94c5338a3647bc2e85ff75d9cf36 upstream.

    A high speed control or bulk endpoint may have bInterval set to zero,
    which means it does not NAK. If bInterval is non-zero, it means the
    endpoint NAKs at a rate of 2^(bInterval - 1).

    The xHCI code to compute the NAK interval does not handle the special
    case of zero properly. The current code unconditionally subtracts one
    from bInterval and uses it as an exponent. This causes a very large
    bInterval to be used, and warning messages like these will be printed:

    usb 1-1: ep 0x1 - rounding interval to 32768 microframes, ep desc says 0 microframes

    This may cause the xHCI host hardware to reject the Configure Endpoint
    command, which means the HS device will be unusable under xHCI ports.

    This patch should be backported to kernels as old as 2.6.31, that contain
    commit dfa49c4ad120a784ef1ff0717168aa79f55a483a "USB: xhci - fix math in
    xhci_get_endpoint_interval()".

    Reported-by: Vincent Pelletier <plr.vincent@gmail.com>
    Suggested-by: Alan Stern <stern@rowland.harvard.edu>
    Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    drivers/usb/host/xhci-mem.c | 2 ++
    1 file changed, 2 insertions(+)

    --- a/drivers/usb/host/xhci-mem.c
    +++ b/drivers/usb/host/xhci-mem.c
    @@ -1250,6 +1250,8 @@ static unsigned int xhci_microframes_to_
    static unsigned int xhci_parse_microframe_interval(struct usb_device *udev,
    struct usb_host_endpoint *ep)
    {
    + if (ep->desc.bInterval == 0)
    + return 0;
    return xhci_microframes_to_exponent(udev, ep,
    ep->desc.bInterval, 0, 15);
    }



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