Re: [RFC]Is usb port number fixed?

From: Greg KH
Date: Fri Apr 20 2012 - 12:19:57 EST

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On Fri, Apr 20, 2012 at 09:39:37PM +0530, Anil Nair wrote:
> >USB ports on a hub are all enumerated the same, but the root hubs
> >aren't, and sometimes hubs on the same bus are not as well.
>   Does every device assigned a port number serially, that is in increasing
> order?


>   If a USB port number is assigned to a USB device then are other USB devices
> able to use it,
>   if connected USB device is Disconnected?

It can, why? USB devices don't care about their device number.

> >But usually, things do come up in the same way all the time, so
> >depending on your use case, you can rely on this, but it is recommended
> >that you look for something else a bit more unique, like a serial number
> >on a device (if it is present), if you wish to uniquely identify a
> >device all the time.
>   Does the Linux Kernel keeps the history of connected devices? So that next
> time,   the same USB device get assigned the same USB port number.

No. I think you are confusing port number with the USB device number,
both of which mean nothing to a USB device at all, and they shouldn't to
anyone else.

greg k-h
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