xhci: Do not drop and add bits in xhci

Drop and Add bits reset the data toggle for high-speed devices in XHCI.
The toggle bit represents the sequence number in USB 2.0 transfers. However,
a device can only recognize that the toggle bit has been reset while in
the HALT state. As a result, the host and device toggle values may
become mismatched, causing xHCI to reject the packet. This issue was
observed while testing the EZ-USB FX2 device.

The transfer may then return to the original value after a
bi-directional TD because the toggle field is only one bit wide. This
explains the reson that we can only receive packets bi-transfer in some
case. Therefore, we do not reset the toggle bit here.

Reviewed by:    adrian
MFC after:      2 weeks
Sponsored by:   The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D57146

sys/dev/usb/controller/xhci.c

@@ -3898,10 +3898,8 @@ xhci_configure_reset_endpoint(struct usb_xfer *xfer)
 	 */
 	switch (xhci_get_endpoint_state(udev, epno)) {
 	case XHCI_EPCTX_0_EPSTATE_DISABLED:
-		drop = 0;
-		break;
 	case XHCI_EPCTX_0_EPSTATE_STOPPED:
-		drop = 1;
+		drop = 0;
 		break;
 	case XHCI_EPCTX_0_EPSTATE_HALTED:
 		err = xhci_cmd_reset_ep(sc, 0, epno, index);
@@ -3910,9 +3908,15 @@ xhci_configure_reset_endpoint(struct usb_xfer *xfer)
 			DPRINTF("Could not reset endpoint %u\n", epno);
 		break;
 	default:
-		drop = 1;
+		/*
+		 * xHCI spec 4.6.8:
+		 * The Drop and Add operation resets the toggle bit, which can
+		 * cause a toggle mismatch between the device and host. As a
+		 * result, xHCI may refuse to receive or process the packet.
+		 */
 		err = xhci_cmd_stop_ep(sc, 0, epno, index);
-		if (err != 0)
+		drop = (err != 0);
+		if (drop)
 			DPRINTF("Could not stop endpoint %u\n", epno);
 		break;
 	}