xhci-ring: "needs XHCI_TRUST_TX_LENGTH quirk" in kernel log

[Eli Billauer <eli.billauer@gmail.com>]

Hello,

Connecting a custom designed (on FPGA) USB 3.0 device to a Renesas 
uPD720202 (1912:0015) and kernel v5.3.0, I get a lot of messages in the 
kernel log, while transmitting data at a high bandwidth through a BULK 
IN endpoint:

handle_tx_event: 36590 callbacks suppressed
xhci_hcd 0000:03:00.0: WARN Successful completion on short TX for slot 1 
ep 18: needs XHCI_TRUST_TX_LENGTH quirk?
(last message repeated several times)

The driver in charge, as reported by lspci, is xhci_hcd.

Probably relevant details:

* The buffer size of the USB transactions is 32 kiB and up (with 
libusb). With e.g. 16 kiB buffers these log messages don't appear.
* The device produces short packets occasionally. When only full-length 
packets are sent, these log messages don't appear.
* Other than these log messages, everything works fine. In particular, 
there are no errors in the data exchange in either situation.
* This problem doesn't happen when running the same test on an Intel 
B150 chipset’s USB 3.0 xHCI controller (8086:a12f).

I don't really know what this warning means, but this whole thing 
kind-of reminds the "WARN Event TRB for slot x ep y with no TDs queued" 
issue that was solved recently. Just a wild guess.

Any idea how this can be fixed?

Thanks and regards,
    Eli