Comment 41 for bug 363812

The following might help debug the problem:

dmesg shows that in fact the card IS detected during boot, the proper modules -cdc_acm and cdc_wdm- load and create the appropriate comm ports, but after a while the usb port is disconnected and ehci_hcd appears unhappy.

I have noted that in kernel 2.27.11 in my distribution (Ubuntu) the ehci_hcd was built as a module, whereas from 2.28.11 on it was built into the kernel.

.....
[ 3.920054] usb 2-4: new high speed USB device using ehci_hcd and address 2
....
[ 4.768172] usb 2-4: configuration #1 chosen from 2 choices
[ 4.816828] cdc_acm 2-4:1.1: ttyACM0: USB ACM device
[ 4.817162] cdc_wdm 2-4:1.5: cdc-wdm0: USB WDM device
[ 4.821853] usb0: register 'cdc_ether' at usb-0000:00:1d.7-4, CDC Ethernet
Device, 02:80:37:ec:02:00
[ 4.821869] usbcore: registered new interface driver cdc_ether
[ 4.822052] cdc_acm 2-4:1.3: ttyACM1: USB ACM device
[ 4.822520] cdc_wdm 2-4:1.6: cdc-wdm1: USB WDM device
[ 4.822532] usbcore: registered new interface driver cdc_wdm
[ 4.822668] cdc_acm 2-4:1.9: ttyACM2: USB ACM device
[ 4.823902] usbcore: registered new interface driver cdc_acm
[ 4.823904] cdc_acm: v0.26:USB Abstract Control Model driver for USB modems
and ISDN adapters
......
[ 9.840181] usb 2-4: USB disconnect, address 2
[ 9.841912] ehci_hcd 0000:00:1d.7: dma_pool_free buffer-2048, f5f48000/35f48000 (bad dma)
[ 9.842038] ehci_hcd 0000:00:1d.7: dma_pool_free buffer-2048, f5f48080/35f48080 (bad dma)