Oleksandr and myself have been looking into why when we enable the
write-back cache on the PandaBoard there are kernel panics with USB. We
have tracked it down to an issue appending the ehci_qh_t to the list at
the end of ehci_setup_standard_chain().

I have a patch at [1] that allows me to run sha256 on a 40MB file over
NSF using the built in smsc USB ethernet chip. The problem is I have
had to place a call to DELAY before EHCI_APPEND_QH. This is obviously
not the correct solution.

Is anyone able to help me narrow down what is missing? It appears to be
a missing cache invalidate or flush somewhere but I haven't been able
to track down what cache function the DELAY is working around.


[1] http://fubar.geek.nz/files/freebsd/ehci_4.diff
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