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how to interpret lsusb output

I'm trying to figure out something about the USB ports on a Debian/Jesse AMD64 server. There are two USB 3.0 ports on the back - at least that's how the manufacturer (Asrock) labels them. When I do a simple lsusb, I get: 

# lsusb
Bus 005 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 009 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 008 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 004 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 007 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 003 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 006 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 002 Device 002: ID 1058:0820 Western Digital Technologies, Inc.
Bus 002 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub

which shows a WD external drive attached. Lsusb -t gives more details:

# lsusb -t
/:  Bus 09.Port 1: Dev 1, Class=root_hub, Driver=ohci-pci/4p, 12M
/:  Bus 08.Port 1: Dev 1, Class=root_hub, Driver=ohci-pci/2p, 12M
/:  Bus 07.Port 1: Dev 1, Class=root_hub, Driver=ohci-pci/5p, 12M
/:  Bus 06.Port 1: Dev 1, Class=root_hub, Driver=ohci-pci/5p, 12M
/:  Bus 05.Port 1: Dev 1, Class=root_hub, Driver=ehci-pci/4p, 480M
/:  Bus 04.Port 1: Dev 1, Class=root_hub, Driver=ehci-pci/5p, 480M
/:  Bus 03.Port 1: Dev 1, Class=root_hub, Driver=ehci-pci/5p, 480M
/:  Bus 02.Port 1: Dev 1, Class=root_hub, Driver=xhci_hcd/4p, 5000M
    |__ Port 2: Dev 2, If 0, Class=Mass Storage, Driver=usb-storage, 5000M
/:  Bus 01.Port 1: Dev 1, Class=root_hub, Driver=xhci_hcd/4p, 480M
The drive is attached to the upper port on a two-port USB socket. If I attach it to the lower port, it shows up attached to Bus 01 as a 480M device.
Am I correct in believing that only the upper port can operate at the full USB3 speed while the lower port is limited to USB2 speeds even though the port is labeled as USB3 and seems to be an xhci device? 

Also, what are the /4p, /2p, etc. after the Driver=?

Thanks in advance.
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