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

[Jack]

Top posting because this is just an interim update - no new real info  
yet.

I think part of my problem is that i don't have any real USB3 device to  
test with.  It might end up being reasonable for a USB2 device plugged  
into a USB3 port to show up connected to a USB2 hub - but that hub is  
actually part of the USB3 host controller.  I have a real USB3 thumb  
drive arriving soon, so we'll see how that shows up when I connect it.

Separate but related is my new webcam, which shows up as a USB2 device,  
although lsusb -v says it is capable of SuperSpeed, which would imply  
USB3.  I have other problems with that device, so I'm not really sure I  
trust anything it says about itself.  I may start a separate thread  
about it, but not without more research first.

Jack

On 2020.09.24 15:35, Sid Spry wrote:
> On Tue, Sep 22, 2020, at 7:11 PM, Jack wrote:
> > 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.
> >
>
> Even high end motherboards tend to only bring out 1 or 2 root hubs.
> That the
> chip supports 4 root hubs does not mean all of them were used.
> Typically there
> are two groups of USB3 and one or two groups of USB2.
>
> Sometimes it's just one USB3 root hub and they attach all of the USB2
> ports to
> it, making everything run at USB2 speeds.
>
> With USB2, hubs are required to have a translation unit that speeds
> USB1
> packets up to USB2 speeds. Even with these translators you can incur
> delays
> waiting for slower USB1 devices to respond as they will take ~4x
> longer, and
> then the buffered data is sped up when it is put on the bus.
>
> With USB3 there is no such requirement. This would be fine as the
> USB2 is
> on separate wires but most USB3 silicon seems to be implemented in
> such a
> way that USB2 transactions slow down the USB3 transactions. In some
> cases
> this is visible with `lsusb -t`: putting a USB2 device on a USB3 bus
> will
> downgrade all devices to USB2 speeds (showing USB3 devices that were
> 5000M as 480M), and even if it is not visible, you may see transfers
> take ~10x
> as long.
>
> I found all of this out when benchmarking flash drives. My
> motherboard was
> wired such that every important USB3 port shared the keyboard and
> mouse
> ports. If you plug a USB1.1/USB2 keyboard and mouse in, everything
> else
> slows down.
>
> USB3.1 I think explicitly addresses this issue saying that USB3
> should always
> run at USB3 speeds, but vendors still seem to be churning out broken
> motherboards.
>
> > 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
> >
>
> I am pretty sure the pairs of ports are linked. This seems to be a new
> development, and I'm not really sure what it means yet.
>
> > 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.
> >
>
> Your motherboard technically isn't miswired per the USB spec. But it
> is
> miswired in the sense de facto none of your ports may support USB3.
>
> You'd have to do more testing yourself to ensure your system is broken
> in the same way mine is, but it is definitely possible. If you get a
> response
> from the manufacturers please let me know what it was.
>
> I have a cheap Intel embedded system with this same problem, and a
> B350 system from ASRock with suspicious USB3 behavior that I haven't
> been able to investigate well.
>
> Cheers.
>
> P.S.: Another funny one I have is a B350 motherboard having enough
> VFIO groups to do GPU passthrough, but arranged explicitly so you
> can't compartmentalize devices. Everything except the NVMe port is
> in one giant group.
>
> Sounds like false advertising to me.
>
>
>