Thinkpad X220 and USB3 on Series 3 Docks *PIC Warning*

[dr_st]

In the following post ansible212 posted some results showing that the USB3 port on the Series 3 Docks with USB3 functions as USB3 when used with a Thinkpad X220 i7 model:
T520 & USB 3.0

This came as a surprise to many, myself included, as the USB3 controller on the X220 is a separate chip, and it was generally assumed that only chipset USB ports are wired to the docks.

Recently I managed to obtain a Mini-Dock Series 3 with USB 3.0 (4337-15U) and test it myself. The results are fully confirmed - USB3 port on the dock works as USB3, but in the process I discovered an interesting thing about the docks.

The original Mini-Dock Series 3 (4337-10U) contains a 6-port USB2 hub. I originally assumed that the USB3 variant used a 5-port hub and a separate USB3 pass-through, but that is not the case. It still contains the same 6-port hub, except that one of the ports also has USB3 lanes.

On the X220 i5, the dock hub hangs off one of the ports of the Intel chipset USB2 controller, and the USB3 lanes of the port are simply not connected.

On the X220 i7, the dock hub hangs off the second port of the NEC USB3 controller. Consider the snapshot from USBView:


The "USB xHCI Compliant Host Controller" (1033:0194) is the NEC uPD720200. Port 1 is the chassis USB3, Port 2 is the Mini-dock USB3. Both have USB3 flash drives devices connected. Port 3 is the USB2 PHY of Port1. Any USB2 devices connected to said port would show up there. Finally, Port4 is the USB2 PHY of Port2, and this is where the 6-port hub of the Mini-Dock is connected (with another hub on port 2, and a USB2 flash drive connected on port 4. Should a USB2 device be plugged into the USB3 port of the dock (or should the dock be used with a USB2-only laptop), it would show up on port 5 here.

This means an interesting thing - on an X220 i7, the USB ports on the docks (even USB2) will not function if the driver for the NEC USB3 controller is not installed. Not a big deal today, as recent operating systems have this driver built-in.

Another curious thing: The X220 Ultrabase also has a USB hub (4-port), but it hangs off a different port in the laptop. The X220 (and also X230) route two separate USB ports through the docking connector - one of which is used in the Ultrabase, and the other in the docks. To the best of my knowledge, they are unique in this regard (based on what I saw in the schematics for X220, X230, T420s and W520).

Edit: Thanks to mpcook, the mystery of the Mini-Dock Plus with USB3 (4338-15U/35U) has been solved as well. On that dock the USB3 port replaces the eSATA connector, and there are still 6 separate USB2 ports. As shown in this post, that dock uses a 7-port USB hub.

[ansible212]

In the following post ansible212 posted some results showing that the USB3 port on the Series 3 Docks with USB3 functions as USB3 when used with a Thinkpad X220 i7 model:
T520 & USB 3.0

This came as a surprise to many, myself included, as the USB3 controller on the X220 is a separate chip, and it was generally assumed that only chipset USB ports are wired to the docks.

Oh ye of little faith LOL