git: 28d85db46b48 - main - xhci: Do not drop and add bits in xhci

The branch main has been updated by aokblast:

URL: https://cgit.FreeBSD.org/src/commit/?id=28d85db46b484589e2ee74cf4b270db066821de1

commit 28d85db46b484589e2ee74cf4b270db066821de1
Author:     ShengYi Hung <aokblast@FreeBSD.org>
AuthorDate: 2026-05-21 12:49:42 +0000
Commit:     ShengYi Hung <aokblast@FreeBSD.org>
CommitDate: 2026-05-22 07:41:07 +0000

    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 | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/sys/dev/usb/controller/xhci.c b/sys/dev/usb/controller/xhci.c
index 3dad0985b39d..b522c5fdc5a3 100644
--- a/sys/dev/usb/controller/xhci.c
+++ b/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;
 	}