Unfortunately the fix seems to be incomplete for me. $ cat /proc/version_signature Ubuntu 2.6.32-28.55-generic 2.6.32.27+drm33.12 $ uname -a Linux ubuntu 2.6.32-28-generic #55-Ubuntu SMP Mon Jan 10 21:21:01 UTC 2011 i686 GNU/Linux Reverting the commit 55b5b5448771f964776a716227afd3ddef2c860e does help, but it appears that another regression has appeared in the meantime. After about 18h I start getting this error from digitemp (I am calling it from cron once every 15min) Error 5: DS2480B Adapter Not Detected Error 10: Read COM Failed Error 10: Read COM Failed Error 10: Read COM Failed Error 10: Read COM Failed Error 10: Read COM Failed Error 10: Read COM Failed Error 10: Read COM Failed Error 10: Read COM Failed Error 10: Read COM Failed Once the system gets into this state, it persists until reboot. I do not see this problem with 2.6.32-26-generic, patched so that 55b5b5448771f964776a716227afd3ddef2c860e is reverted. lsusb still sees the device: $ lsusb Bus 005 Device 003: ID 046d:c03d Logitech, Inc. M-BT96a Pilot Optical Mouse Bus 005 Device 002: ID 0403:6001 Future Technology Devices International, Ltd FT232 USB-Serial (UART) IC Bus 005 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub Bus 004 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub Bus 003 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub Bus 002 Device 003: ID 413c:2003 Dell Computer Corp. Keyboard Bus 002 Device 002: ID 03f0:3611 Hewlett-Packard PSC 2410 PhotoSmart Bus 002 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub $ sudo lsusb -v -d 0403:6001 Bus 005 Device 002: ID 0403:6001 Future Technology Devices International, Ltd FT232 USB-Serial (UART) IC Device Descriptor: bLength 18 bDescriptorType 1 bcdUSB 2.00 bDeviceClass 0 (Defined at Interface level) bDeviceSubClass 0 bDeviceProtocol 0 bMaxPacketSize0 8 idVendor 0x0403 Future Technology Devices International, Ltd idProduct 0x6001 FT232 USB-Serial (UART) IC bcdDevice 6.00 iManufacturer 1 FTDI iProduct 2 FT232R USB UART iSerial 3 A900a3DX bNumConfigurations 1 Configuration Descriptor: bLength 9 bDescriptorType 2 wTotalLength 32 bNumInterfaces 1 bConfigurationValue 1 iConfiguration 0 bmAttributes 0xa0 (Bus Powered) Remote Wakeup MaxPower 90mA Interface Descriptor: bLength 9 bDescriptorType 4 bInterfaceNumber 0 bAlternateSetting 0 bNumEndpoints 2 bInterfaceClass 255 Vendor Specific Class bInterfaceSubClass 255 Vendor Specific Subclass bInterfaceProtocol 255 Vendor Specific Protocol iInterface 2 FT232R USB UART Endpoint Descriptor: bLength 7 bDescriptorType 5 bEndpointAddress 0x81 EP 1 IN bmAttributes 2 Transfer Type Bulk Synch Type None Usage Type Data wMaxPacketSize 0x0040 1x 64 bytes bInterval 0 Endpoint Descriptor: bLength 7 bDescriptorType 5 bEndpointAddress 0x02 EP 2 OUT bmAttributes 2 Transfer Type Bulk Synch Type None Usage Type Data wMaxPacketSize 0x0040 1x 64 bytes bInterval 0 Device Status: 0x0000 (Bus Powered) The device node seems to have normal permissions $ ls -l /dev/ttyUSB0 0 crw-rw---- 1 root dialout 188, 0 2011-01-29 20:50 /dev/ttyUSB0 stracing with the device in this state shows digitemp (3.5.0ds1-1ubuntu1) trying to select() a file descriptor (with the same arguments as in the working case,) and timing out. straces for both kernels are attached. If I unplug and replug the device I see this in syslog: [71833.368048] usb 5-1: USB disconnect, address 2 [71833.368231] ftdi_sio ttyUSB0: FTDI USB Serial Device converter now disconnected from ttyUSB0 [71833.368252] ftdi_sio 5-1:1.0: device disconnected [71837.328016] usb 5-1: new full speed USB device using uhci_hcd and address 4 [71837.526685] usb 5-1: configuration #1 chosen from 1 choice [71837.534634] ftdi_sio 5-1:1.0: FTDI USB Serial Device converter detected [71837.534671] usb 5-1: Detected FT232RL [71837.534674] usb 5-1: Number of endpoints 2 [71837.534676] usb 5-1: Endpoint 1 MaxPacketSize 64 [71837.534679] usb 5-1: Endpoint 2 MaxPacketSize 64 [71837.534681] usb 5-1: Setting MaxPacketSize 64 [71837.535923] usb 5-1: FTDI USB Serial Device converter now attached to ttyUSB0 and the device is working again.