A RPi4 xHCI VL805 problem that needs to be avoided: "xhci: quirks: add link TRB quirk for VL805"

[Mark Millard]

https://github.com/raspberrypi/linux/pull/3929 reports:

QUOTE
The VL805 controller can't cope with the TR Dequeue Pointer for an endpoint
being set to a Link TRB. The hardware-maintained endpoint context ends up
stuck at the address of the Link TRB, leading to erroneous ring expansion
events whenever the enqueue pointer wraps to the dequeue position.

If the search for the end of the current TD and ring cycle state lands on
a Link TRB, move to the next segment.
END QUOTE

Also: Dealing with the link trb also toggling the ring cycle state
is something to watch for according to the later notes.

===
Mark Millard
marklmi at yahoo.com
( dsl-only.net went
away in early 2018-Mar)