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    Subject[PATCH 3.16 269/305] xhci: Prevent U1/U2 link pm states if exit latency is too long
    3.16.63-rc1 review patch.  If anyone has any objections, please let me know.

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

    From: Mathias Nyman <mathias.nyman@linux.intel.com>

    commit 0472bf06c6fd33c1a18aaead4c8f91e5a03d8d7b upstream.

    Don't allow USB3 U1 or U2 if the latency to wake up from the U-state
    reaches the service interval for a periodic endpoint.

    This is according to xhci 1.1 specification section 4.23.5.2 extra note:

    "Software shall ensure that a device is prevented from entering a U-state
    where its worst case exit latency approaches the ESIT."

    Allowing too long exit latencies for periodic endpoint confuses xHC
    internal scheduling, and new devices may fail to enumerate with a
    "Not enough bandwidth for new device state" error from the host.

    Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    [bwh: Backported to 3.16: adjust context, indentation]
    Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
    ---
    drivers/usb/host/xhci.c | 16 ++++++++++++++++
    1 file changed, 16 insertions(+)

    --- a/drivers/usb/host/xhci.c
    +++ b/drivers/usb/host/xhci.c
    @@ -4466,9 +4466,25 @@ static u16 xhci_call_host_update_timeout
    u16 *timeout)
    {
    if (state == USB3_LPM_U1) {
    + /* Prevent U1 if service interval is shorter than U1 exit latency */
    + if (usb_endpoint_xfer_int(desc) || usb_endpoint_xfer_isoc(desc)) {
    + if (xhci_service_interval_to_ns(desc) <= udev->u1_params.mel) {
    + dev_dbg(&udev->dev, "Disable U1, ESIT shorter than exit latency\n");
    + return USB3_LPM_DISABLED;
    + }
    + }
    +
    if (xhci->quirks & XHCI_INTEL_HOST)
    return xhci_calculate_intel_u1_timeout(udev, desc);
    } else {
    + /* Prevent U2 if service interval is shorter than U2 exit latency */
    + if (usb_endpoint_xfer_int(desc) || usb_endpoint_xfer_isoc(desc)) {
    + if (xhci_service_interval_to_ns(desc) <= udev->u2_params.mel) {
    + dev_dbg(&udev->dev, "Disable U2, ESIT shorter than exit latency\n");
    + return USB3_LPM_DISABLED;
    + }
    + }
    +
    if (xhci->quirks & XHCI_INTEL_HOST)
    return xhci_calculate_intel_u2_timeout(udev, desc);
    }
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