[Bug 299163] xhci: Etron EJ168 requires IOC disabled on Link TRBs

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=299163

--- Comment #1 from Guy Wyers <guy.wyers@gmail.com> ---
Further testing has identified a problem with the proposed workaround.

With an unmodified 15.1-RELEASE-p3 kernel, the RTL8156 attached through the
EJ168 falls back to USB High-Speed (480 Mbps), but sustained iperf3 traffic is
stable for 30 seconds in both directions (317 Mbps host RX, 213 Mbps host TX).

With the proposed NO_LINK_IOC quirk, the same device enumerates successfully at
SuperSpeed and initially transfers at approximately 940–950 Mbps. However,
sustained host RX causes the interface to fail after several seconds. The USB
device remains attached at SuperSpeed, while the network interface enters
repeated link-state DOWN/UP transitions and subsequent transmissions fail with
ENOBUFS.

I am therefore marking the current patch obsolete while investigating the EJ168
SuperSpeed/xHCI behaviour further. The original control-transfer issue remains
reproducible, and disabling IOC on the two Link TRBs remains sufficient to make
SuperSpeed enumeration succeed, but the workaround is not yet suitable for
inclusion.

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