[gentoo-user] USB problem/questions (not Gentoo specific)

[Jack]

I've got a Ryzen 5 2600 in an MSI B350 Tomahawk motherboard.  The specs  
imply that the CPU produces four USB 3.0 ports and the chipset produces  
6 USB 2.0 and four USB 3.1 (although the last four are not available  
with this motherboard.

lsusb shows
Bus 004 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
Bus 003 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
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

lsusb -t shows
/:  Bus 04.Port 1: Dev 1, Class=root_hub, Driver=xhci_hcd/4p, 5000M
/:  Bus 03.Port 1: Dev 1, Class=root_hub, Driver=xhci_hcd/4p, 480M
/:  Bus 02.Port 1: Dev 1, Class=root_hub, Driver=xhci_hcd/4p, 10000M
/:  Bus 01.Port 1: Dev 1, Class=root_hub, Driver=xhci_hcd/10p, 480M

Bus 01 shows 10p because there is a 4 port external hub connected, so  
that should be the 6 USB 2.0 ports - two rear ports, and two two port  
headers (JUSB1 and JUSB2)
Bus 02 is (I assume) advertised by the B350 chipset, but I don't expect  
it to show up on any physical ports or headers
Bus 03 is a mystery, as I have no idea where the extra USB 2.0 ports  
are coming from
Bus 04 should be the USB 3.0 generated by the CPU, and I assume should  
be what feeds the JUSB3 and JUSB4 USB3 headers

The rear IO panel has 2 USB 2.0 ports, and if I plug anything into  
them, they show up as ports 8 and 9 on bus 1.
The front of the case has two USB3 ports, which show up on the bus 1,  
ports 1 and 2 if the connector is in JUSB4 on the mobo, or ports 3 and  
4 if using JUSB3.
The three Type-A USB3 connectors on the back show up on bus 3, ports 1,  
2, and 4, with port 3 presumably being the Type-C connector.  I don't  
have anything to test in the Type-C port.

I'd be really surprised if the back IO panel on the mobo is miswired,  
but why are the supposed USB3 ports all showing up as USB2?  I have one  
webcam capable of USB3, but it's only connecting at 480M (per lsusb -v)  
but it's plug shows the standard USB logo, not the superspeed version.

I've had no response to my query on the MSI user forum, and none yet to  
my ticket to MSI tech support.

Any suggestions on where to go from here?  I'll be glad to post more,  
but don't want to spam the list with irrelevant logs.

Thanks for any ideas.

Jack