All USB ports on motherboard running through the same bus

Question

I have a Gigabyte H87-HD3 motherboard. According to the specification it supports up to 8 USB 2.0/1.1 ports. Now I try to connect a device that is non-compatible with USB 3.0. It does not work on any of the USB ports, neither directly on the board nor on the case, neither blue USB 3.0 ports or others.

While trying to get my device to work, it appeared to me that all of the ports are routed to the same controller and I am wondering if this is correct. I am on Ubuntu, this is the output of lsusb -t:

/:  Bus 04.Port 1: Dev 1, Class=root_hub, Driver=xhci_hcd/6p, 5000M
/:  Bus 03.Port 1: Dev 1, Class=root_hub, Driver=xhci_hcd/14p, 480M
    |__ Port 5: Dev 2, If 0, Class=Human Interface Device, Driver=usbhid, 12M
    |__ Port 5: Dev 2, If 1, Class=Human Interface Device, Driver=usbhid, 12M
    |__ Port 5: Dev 2, If 2, Class=Human Interface Device, Driver=usbhid, 12M
/:  Bus 02.Port 1: Dev 1, Class=root_hub, Driver=ehci-pci/2p, 480M
    |__ Port 1: Dev 2, If 0, Class=Hub, Driver=hub/8p, 480M
/:  Bus 01.Port 1: Dev 1, Class=root_hub, Driver=ehci-pci/2p, 480M
    |__ Port 1: Dev 2, If 0, Class=Hub, Driver=hub/6p, 480M

As you can see, Bus 03 has an xHCI driver, the speed is USB 2.0-like. No matter where I connect my devices, they always appear under Bus 03. I tried this with both Ubuntu and Windows 10, so I do not think that this is a software issue.

Could someone clarify this to me? Does the board route everything to the same Bus? Is there no proper USB 2.0 support despite the specification?

Answer 1

You very clearly have 4 different busses. The USB 3.0 (XHCI) controller shows up on two busses (busses 3 and 4). That's for compatibility reasons, the USB 2.0/1.0 part of the controller gets a different bus.

On bus 1 and 2 are two USB 2.0 (EHCI) controllers, each with two ports, one of which is probably a debug port which is not connected (see dmesg), and one is directly connected to an integrated hub each (one with 6 ports on bus 1, and one with 8 ports on bus 2).

So if you look at lspci, you should see 3 USB controllers, one XHCI and two EHCI. Very likely the EHCI controllers are in the Southbridge (check the address).

The datasheet for the Gigabyte H87-HD3 says

Up to 6 USB 3.0/2.0 ports (4 ports on the back panel, 2 ports available through the internal USB header)
Up to 8 USB 2.0/1.1 ports (2 ports on the back panel, 6 ports available through the internal USB headers)

So the 6 USB 3.0 ports are where they belong, and 6 of those ports are also on bus 3 in USB 2.0 compatibility mode.

Now it's possible that the XHCI controller has 8 extra USB 2.0 ports (google the data sheet and check), and the board designers only used those ports, and ignored the additional 14 ports that are likely on the Southbridge. In that case, indeed all ports would be routed through a single controller, and if you have a USB device that for some reason doesn't like this particular controller, you may be out of luck.

But it's impossible to say that definitely, though if you plugged a working USB 2.0 device in turn into each of the 14 ports, and it showed up on bus 3 in every case, with a different port number, it starts to sound very likely.

Have you tried to connect an external hub to one port, and connect the "difficult" device to that hub? That may help.