On Thu, 14 May 2009, Ethan wrote:
> I'm having trouble with a 7-port, powered USB hub made by D-Link
> (model DUB-7). The devices plugged into the hub seem to work fine for
> small transfers, but large transfers (such as to/from a scanner or
> usb-storage device) break something. Once things are "broken" I see
> from the syslog that the bus is reset every few seconds. It is not
> clear to me if any data moves at all between bus resets but it is very
> little if anything. When the bus is in this state, all devices on the
> bus become inaccessible not just the one that was engaged in the
> transfer. Removing and reinstalling the ehci_hcd and ohci_hcd modules
> seems to reset the bus and correct the problem until the next large
> transfer is initiated.
Unplugging the troublesome hub and plugging it back in will most likely
work just as well.
> I suspect the problem lies with the hub because all of the devices
> work fine when plugged directly into the computer or when plugged into
> a different brand hub.
>
> The linux kernel version is 2.6.26. The computer is AMD64 based with
> an AMD SB700 southbridge. The hub is D-Link model DUB-7.
>
> Does the linux hub driver have any parameters that I can try tweaking?
No. Well yes, but they have nothing to do with your problem. They
control the procedure used for initializing newly-detected USB devices.
> I can't seem to find much documentation on it.
Look for the entries marked USB in Documentation/kernel-parameters.txt.
Or look through the beginning of the source file for the hub driver:
drivers/usb/core/hub.c. The module parameters are easy to spot.
> Can anyone suggest
> other troubleshooting steps?
You might try testing the hub with a different computer or a different
operating system or a different USB cable. For example, it would be
interesting to know if Windows has no trouble using the hub. (Although
I don't see how we could make use of that information without knowing
the exact mechanism causing the problem.)
Alan Stern
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