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

From: Robert de Rooy
Date: Mon Jun 11 2007 - 16:43:14 EST

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.

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