Messages in this thread | | | Date | Mon, 23 Apr 2012 11:13:06 -0400 (EDT) | From | Alan Stern <> | Subject | Re: [RFC]Is usb port number fixed? |
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On Mon, 23 Apr 2012, Wang YanQing wrote:
> On Sun, Apr 22, 2012 at 08:47:24AM -0400, Alan Stern wrote: > > On Sun, 22 Apr 2012, Anil Nair wrote: > > > > > The port number comes from root hub managed by the host controller. Its > > > fixed dynamically during enumeration, and can change. > > > Please correct me if i am wrong. > > > > You are indeed wrong. Port numbers are not fixed dynamically and they > > cannot change. > Right?
Right.
> Could you pin out the codes in kernel?
I don't understand the question. What code in the kernel do you want to see?
> > On the other hand, bus numbers _are_ assigned dynamically and they can > > (and do) change. > > > Indeed, I never meat the situation lspci output different bus number on the same machine. > Any more comment?
Try unloading ehci-hcd, uhci-hcd, and ohci-hcd, and then reloading them in different orders. Depending on what sort of hardware you have, the bus numbers will change.
On Mon, 23 Apr 2012, Anil Nair wrote:
> You meant to say port numbers are fixed but bus address changes > dynamically, also does the host controller > fixes the port number?
Yes.
> If USB Bus bandwidth is not available, how does it > assign port numbers?
The port numbers are determined by the hardware -- each set of wires has its own port number. The numbers have nothing to do with bandwidth.
Alan Stern
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