[LAU] Sound Devices USBPre2, UAC2 status

[shal at free.fr]

Hi,

Some old posts exist about the UAC2 support for the Sound Devices USBPre2 but some problem remains.
The current status is that this sound card is supported as a USB 1.1 card in high-speed mode.
But this card is not seen as a Usb Audio Class 2 on  Linux. On Mac OS X this card is recognized as UAC2.


My principal problem is that the "device descriptor" provided by the card is always a USB1.1 class
There is two modes of boot for the card (pressing the "1" button, the card is in full speed mode, without pressing in UAC2 mode)
There is only one difference between these two modes in the lsusb -v : the "bInterval" go to 4 from 1.

This is already view by Clemens on: 
http://lists.linuxaudio.org/pipermail/linux-audio-user/2011-October/081275.html

In this another post, we can seen:

Bernardo Barros wrote:
> Ok, I reconnected without pressing "1".
> 
> Bus 002 Device 002: ID 0926:0202
> Device Descriptor:
>   bNumConfigurations      2

Strange, I have never 2 on bNumConfigurations !   Somebody can test it on its card ?
This is perhaps my problem, my card only provides one "Configuration Descriptor". 
The second one is certainly the UAC2 "Configuration Descriptor".


The lsusb without 1 pressed : http://pastebin.com/8yjjASv7
The lsusb with 1 pressed : http://pastebin.com/pGFdjR4K
The usbmon trace of the insertion of the usbpre2 (without "1")  : http://pastebin.com/pySC4Age

This sound card is great, it is very disappointing to not be able to used it with all functionnalities.

I search help in order to debug this problem.
I am devlopper, I can test kernel patches without problem.

Thank for any idea (or patch).

Olivier