Well, the activity LEDs don't work yet, but check this out:

[ 3490.443830] usb 3-1: new full-speed USB device number 5 using xhci_hcd
[ 3490.593313] usb 3-1: New USB device found, idVendor=10c4, idProduct=ea90, bcdDevice= 0.00
[ 3490.593317] usb 3-1: New USB device strings: Mfr=1, Product=2, SerialNumber=3
[ 3490.593320] usb 3-1: Product: CP2112 HID USB-to-SMBus Bridge
[ 3490.593323] usb 3-1: Manufacturer: Silicon Laboratories
[ 3490.593325] usb 3-1: SerialNumber: 00ACA028
[ 3490.661995] cp2112 0003:10C4:EA90.0002: hidraw1: USB HID v1.01 Device [Silicon Laboratories CP2112 HID USB-to-SMBus Bridge] on usb-0000:08:00.0-1/input0
[ 3490.716377] cp2112 0003:10C4:EA90.0002: Part Number: 0x0C Device Version: 0x03

 Make sure you have i2c-tools installed via whatever package manager you prefer, then:

[user@localhost ~]$ i2cdetect -l
i2c-0    unknown       SMBus I801 adapter at 0400
[snip]
i2c-5    unknown       CP2112 SMBus Bridge on hidraw1

And then:

[user@localhost ~]$ sudo i2cdetect -y -r 5
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:          -- -- -- -- -- -- -- -- -- -- -- -- -- 
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
50: -- -- -- -- -- 55 -- -- -- -- -- -- -- -- -- -- 
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
70: -- -- -- -- -- -- -- -- 

Address 0x55 should be the oscillator - the actual address depends on factory presets requested when ordered. Each preset is assigned a unique 6 digit code which is incorporated into the part number. I ordered from DIgikey (not directly from SiLabs) so it was unclear what the address would be.

If I understand the CP2112 docs correctly, the chip shouldn't show up during an i2cdetect scan. Clearly it's working (otherwise we won't be seeing anything at all) and the datasheet says it should be available at address 0x02.

I think the next goal should be a small/simple utility that just sets the output frequency.