On Mon, 9 Feb 2015, Michael Tessier wrote:

Okay; I did my homeworks. We've loaded kernel V3.16 (Oct 14th, 2015)
on an i.MX51 plattform and the problem is still there. Unless an
important change occured in V3.19, it appears that the latest kernel
is not the solution for us. So we're still not able to use 4 codecs
on our i.MX plattform.

So just to make things clearer:
- We have customers waiting for a solution with that hardware (this
hardware is already delivred AND used);
- We have important comittments and severe penalties ($$$) if we're
not able to deliver on time (due for March 15th);
- We've already looked at a hardware solution, which corresponds to
replace current units ($$$$$), so that is not really an option for
us;

So as a last resort, I'm wondering, where is the USB expert who could
help us solving our problem? Any suggestions?

That would be me.

If we are to get into debugging the USB driver, we would do it with
the current kernel used (V2.6.31). What are the better tools to get
into that? I guess a USB analyzer (hardware) would be the smart
thing? Any brand name to suggest?

It really would be better to start by debugging the most recent kernel
possible.  Once the problem has been solved there, it should be fairly
straightforward to port it back.

Any other ideas for a solution will be really appreciated.

You should begin by using usbmon during a short test (one or two 
seconds ought to be enough).  See the instructions in the kernel source 
file Documentation/usb/usbmon.txt.

Alan Stern