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

On Sat, 9 Jun 2007, Robert de Rooy wrote:

Alan Stern wrote:
Robert, it would help somewhat if you could build a kernel with
CONFIG_USB_DEBUG turned on and post the dmesg log showing what happens
when you plug in one of those non-working devices.

Sorry, yes I should have done that before...

Unfortunately you posted the system log file instead of the dmesg log,
and your syslogd was configured not to retain debug-level messages.

Yes, in principle Linux can be made to switch over to full speed when
high speed fails. But there are limitations: The switchover would work
only for devices plugged directly into the computer, not for devices
plugged into a high-speed hub. And some Linux systems (not regular
PCs) have EHCI implementations that don't allow such a switch -- or
if they do, I'm not aware of how to accomplish it.

Interesting, I have a USB 2.0 hub, but have not tried it, mainly because
I need to find a power supply for it first.
But regardless if the hub works as USB 2.0 or 1.1, it could be that
another hub behaves differently, just like I have one USB 2.0 memory key
that still works as such.

You did not understand my point. Regardless of how the hub behaves,
there is no way to tell it that a device plugged into a particular port
should not be allowed to run at high speed.

Alan Stern

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