Re: [linux-usb-devel] ThinkPad T41 - Strange USB 2.0 behaviour

Robert de Rooy
2007-06-11T20:43:07Z

Alan Stern wrote:
> Okay. It's clear that you've got a hardware problem of some sort.
> Hard to say what it is, but evidently the EHCI controller thinks that
> the device is repeatedly being unplugged and replugged.
>
> Anyway, this isn't a problem of recognizing that a single device is
> having problems. In fact the computer has no way of knowing that a
> single device is involved; all it knows is that _something_ gets
> plugged into the port and then removed. There's no way to tell if it's
> the same _something_ from one iteration to the next.
>
> You can manually force the port to run at full speed instead of high
> speed as follows:
>
> echo '4' >/sys/class/usb_host/usb_host4/companion
>
> The "companion" attribute file contains a list of ports which are
> permanently set to be handled by the EHCI's companion controller. To
> return to high-speed operation, use '-4' instead of '4' above. This
> might or might not solve your problem -- the hardware bug might cause
> the port to return automatically to high-speed regardless.
>
> Let me know what happens.
>
> Alan Stern

Yes that works.
I tried to plug and unplug the device repeatedly and each time it came
up in full-speed mode.