Hi,

I am relatively new to xhci and its driver. I am trying to get a xhci
driver runtime log to understand how it handles usb transactions, but I
don't get much information with dynamic debug (module xhci_hcd) or
enabling xhci trace events. Is there any other methods you guys use to
debug xhci driver?

BTY, the issue I am trying to debug is when reading bulk IN data from a
USB2.0 device, if the device doesn't have data to transmit and NAKs the
IN packet, after 4 pairs of IN-NAK transactions, xhci stops sending
further IN tokens until the next SOF, which leaves ~90us gape on the
bus.

But when reading data from a USB2.0 thumb drive, this issue doesn't
happen, even if the device NAKs the IN tokens, xhci still keeps sending
IN tokens, which is way more than 4 pairs of IN-NAK transactions.

Any one has a clue on what causes xhci to stop sending IN tokens after
the device NAK'd 4 times?

Thanks,
-Bin.
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