Re: Understanding 'lsusb -t'

[Greg KH <greg@kroah.com>]

On Fri, Aug 30, 2024 at 10:25:19AM -0400, Alan Stern wrote:
> On Fri, Aug 30, 2024 at 10:14:20PM +1000, Eyal Lebedinsky wrote:
> > I assume that the generated list is a tree, so each leaf (Device/If) is on only one point.
> > 
> > I note this output:
> > 
> > $ lsusb -tv
> > /:  Bus 001.Port 001: Dev 001, Class=root_hub, Driver=xhci_hcd/16p, 480M
> >     ID 1d6b:0002 Linux Foundation 2.0 root hub
> > [trimmed]
> >     |__ Port 004: Dev 004, If 0, Class=Hub, Driver=hub/4p, 480M
> > [trimmed]
> >     |__ Port 005: Dev 006, If 0, Class=Hub, Driver=hub/4p, 480M
> > [trimmed]
> >     |__ Port 006: Dev 019, If 0, Class=Hub, Driver=hub/4p, 480M
> >         ID 2109:2817 VIA Labs, Inc.
> > /:  Bus 002.Port 001: Dev 001, Class=root_hub, Driver=xhci_hcd/10p, 10000M
> > [trimmed]
> >     |__ Port 006: Dev 006, If 0, Class=Hub, Driver=hub/4p, 5000M
> >         ID 2109:0817 VIA Labs, Inc.
> > 
> > I removed some content that is not relevant to my question.
> > 
> > Note the Bus 001.Port 006 and Bus 002.Port 006 entries.
> > 
> > I verified that both are for the same (one) device. They do not show when I disconnect it.
> > The device is an external 4-port USB3.0 hub. It is listed once as 480M and once as 5000M.
> > Nothing is plugged into any of the four ports.
> > 
> > Is this correct? Why does this device show twice in the list?
> 
> USB 3 actually uses _two_ physical buses.  Each cable has two twisted 
> pairs of wires carrying the SuperSpeed (5000 Mb/s or more) USB-3 data in 
> and out, and also has two wires carrying the legacy USB-2 data (480 Mb/s 
> or less) in and out.
> 
> These physical buses are represented separately in the kernel.  In your 
> example, Bus 001 and Bus 002 use the same cable and the same xHCI host 
> controller; Bus 001 is the legacy USB-2 bus (you can tell by the speed) 
> and Bus 002 is the SuperSpeed bus.

{sigh} I totally missed the 2 different speeds, I was just looking at
the host controller driver type.

I'll blame the jet-lag, but I really should have caught that...

thanks for clearing this up.

greg k-h