[PATCH 3.16 269/305] xhci: Prevent U1/U2 link pm states if exit latency is too long

[Ben Hutchings]

3.16.63-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Mathias Nyman <mathias.ny...@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.ny...@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
[bwh: Backported to 3.16: adjust context, indentation]
Signed-off-by: Ben Hutchings <b...@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);
        }