DragonFlyBSD

Since enabling ehci by default booting with my USB keyboard plugged in has
caused the box to panic almost every time (9 out of 10 or more), when it does
not panic the keyboard works. Prior to this (ohci only) the keyboard would not
work if plugged in during boot almost every time (9 out of 10 or more), but
would work fine every time if plugged in after boot. Plugging it in after boot
still works fine w/ ehci.

The panic in question is panic: ohci_add_done: addr 0x???????? not found, the
call stack includes ohci_intr().

It seems the ohci driver is servicing an interrupt and the conditions are right
to enter ohci_add_done(), but the ohci_hash_find_*'s are unsuccessful.

Adding kprintf's to ohci_hash_add_* and ohci_hash_rem_* cause the box to boot
with a working keyboard a much greater percentage of the time, seemingly
indicating a race / something timing related.