populated. Apparently, if you use an ehci controller, it's not.
Use usbd_device2interface_handle() to retrieve the interface handle.
NOTE: uaa->iface is populated in the probe routine, so I suspect the
fact that it's NULL in the attach routine is a bug in the ehci driver.
Also, don't depend on the PHY addresses returned by the AXE_CMD_READ_PHYID
command. The address is correct for my LinkSys NIC, but a user has
reported that with a D-Link NIC, the PHYID command returns address 4
while the attached Broadcom PHY is in fact strapped for address 0.
Instead, latch onto the first PHY address that returns valid data
during a readreg operation.
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