--- 64cb409f25b67700ce36a51e30b48ad68d5a03c2
+++ dd71f02d5ff4e9b3868e9fb0decf7ed662bce169
@@ -439,47 +439,6 @@ int xhci_setup_addressable_virt_dev(stru
 	return 0;
 }
 
-/*
- * Convert interval expressed as 2^(bInterval - 1) == interval into
- * straight exponent value 2^n == interval.
- *
- */
-static unsigned int xhci_parse_exponent_interval(struct usb_device *udev,
-		struct usb_host_endpoint *ep)
-{
-	unsigned int interval;
-
-	interval = clamp_val(ep->desc.bInterval, 1, 16) - 1;
-	if (interval != ep->desc.bInterval - 1)
-		dev_warn(&udev->dev,
-			 "ep %#x - rounding interval to %d microframes\n",
-			 ep->desc.bEndpointAddress,
-			 1 << interval);
-
-	return interval;
-}
-
-/*
- * Convert bInterval expressed in frames (in 1-255 range) to exponent of
- * microframes, rounded down to nearest power of 2.
- */
-static unsigned int xhci_parse_frame_interval(struct usb_device *udev,
-		struct usb_host_endpoint *ep)
-{
-	unsigned int interval;
-
-	interval = fls(8 * ep->desc.bInterval) - 1;
-	interval = clamp_val(interval, 3, 10);
-	if ((1 << interval) != 8 * ep->desc.bInterval)
-		dev_warn(&udev->dev,
-			 "ep %#x - rounding interval to %d microframes, ep desc says %d microframes\n",
-			 ep->desc.bEndpointAddress,
-			 1 << interval,
-			 8 * ep->desc.bInterval);
-
-	return interval;
-}
-
 /* Return the polling or NAK interval.
  *
  * The polling interval is expressed in "microframes".  If xHCI's Interval field
@@ -497,38 +456,40 @@ static inline unsigned int xhci_get_endp
 	case USB_SPEED_HIGH:
 		/* Max NAK rate */
 		if (usb_endpoint_xfer_control(&ep->desc) ||
-		    usb_endpoint_xfer_bulk(&ep->desc)) {
+				usb_endpoint_xfer_bulk(&ep->desc))
 			interval = ep->desc.bInterval;
-			break;
-		}
 		/* Fall through - SS and HS isoc/int have same decoding */
-
 	case USB_SPEED_SUPER:
 		if (usb_endpoint_xfer_int(&ep->desc) ||
-		    usb_endpoint_xfer_isoc(&ep->desc)) {
-			interval = xhci_parse_exponent_interval(udev, ep);
+				usb_endpoint_xfer_isoc(&ep->desc)) {
+			if (ep->desc.bInterval == 0)
+				interval = 0;
+			else
+				interval = ep->desc.bInterval - 1;
+			if (interval > 15)
+				interval = 15;
+			if (interval != ep->desc.bInterval + 1)
+				dev_warn(&udev->dev, "ep %#x - rounding interval to %d microframes\n",
+						ep->desc.bEndpointAddress, 1 << interval);
 		}
 		break;
-
+	/* Convert bInterval (in 1-255 frames) to microframes and round down to
+	 * nearest power of 2.
+	 */
 	case USB_SPEED_FULL:
-		if (usb_endpoint_xfer_int(&ep->desc)) {
-			interval = xhci_parse_exponent_interval(udev, ep);
-			break;
-		}
-		/*
-		 * Fall through for isochronous endpoint interval decoding
-		 * since it uses the same rules as low speed interrupt
-		 * endpoints.
-		 */
-
 	case USB_SPEED_LOW:
 		if (usb_endpoint_xfer_int(&ep->desc) ||
-		    usb_endpoint_xfer_isoc(&ep->desc)) {
-
-			interval = xhci_parse_frame_interval(udev, ep);
+				usb_endpoint_xfer_isoc(&ep->desc)) {
+			interval = fls(8*ep->desc.bInterval) - 1;
+			if (interval > 10)
+				interval = 10;
+			if (interval < 3)
+				interval = 3;
+			if ((1 << interval) != 8*ep->desc.bInterval)
+				dev_warn(&udev->dev, "ep %#x - rounding interval to %d microframes\n",
+						ep->desc.bEndpointAddress, 1 << interval);
 		}
 		break;
-
 	default:
 		BUG();
 	}