We recently encountered an issue with VMware ESXi USB passthrough that is worth noting. On a Dell PowerEdge R and T series servers (T710, R710, R610, etc) you can opt to install ESXi on the embedded SD card. It works great and allows the OS disk to be completely separate from the datastore disk (which is great if problems arise).  If you want to use VMDirectPath for USB passthrough then you need to be aware that one of the EHCI controllers is where the SD card is connected!  The same controller that feeds the front 2 USB ports is also attached to the internal USB port on the motherboard and the SD card.  If you pass that controller through then 1) the SD card becomes inaccessible to VMware and you will not be able to save any changes on the VMware host, 2) you will not be able to access the /bootbank directory, and 3) if you run “lsusb” you will not see any output.

After some trial and error we found that the EHCI controller at 00:1a:7 is the controller for the front and the controller at 00:1d:7 is the controller for the back.

If you accidentally have forwarded the front USB controller then boot from the ESXi installation media and choose to do a repair install.  Keep in mind that a repair install does not save any host settings, so make sure you take good notes on your network config and any other customizations on the host before running the repair install.  Once you come back up go into the datastore and right click on each .VMX file and add the VMs back into inventory.

If you need to do some discovery on your host to map USB ports to controllers use the lsusb command.  I found this one was particularly useful at filtering out much of the noise.

lsusb -v | grep -e Bus -e iSerial -e iProduct -e bInterfaceClass