Most recent kernel where this bug did not occur: 2.6.15 Distribution: Kubuntu 5.10 (Breezy Badger) Hardware Environment: Laptop MSI S270 (ATIIXP chipset) with mobile Sempron Software Environment: Problem Description: When a USB to RS232 adapter is connected during booting and Legacy USB support is activated in the BIOS, the system never displays [OK] after the "Detecting and activating hardware" sentence. Then the keyboard is still reacting (but you can not do anything to go on booting). In fact I had to turn off my computer the hard way. Other USB devices (tested with USB Bluetooth adapter, USB MMC cardreader and USB mouse) were activated fine by "Detecting and activating hardware". Moreover the USB to serial converter works well when connected after "Detecting and activating hardware" had finished. The dmesg output (with "Legacy USB Support" activated) of the converter connected when the system is already running is: [17181800.648000] usb 1-2: new full speed USB device using ohci_hcd and address 2 [17181800.800000] usb 1-2: configuration #1 chosen from 1 choice [17181800.908000] usbcore: registered new driver usbserial [17181800.908000] drivers/usb/serial/usb-serial.c: USB Serial support registered for generic [17181800.908000] usbcore: registered new driver usbserial_generic [17181800.908000] drivers/usb/serial/usb-serial.c: USB Serial Driver core [17181800.920000] drivers/usb/serial/usb-serial.c: USB Serial support registered for pl2303 [17181800.924000] pl2303 1-2:1.0: pl2303 converter detected [17181800.924000] usb 1-2: pl2303 converter now attached to ttyUSB0 [17181800.924000] usbcore: registered new driver pl2303 [17181800.924000] drivers/usb/serial/pl2303.c: Prolific PL2303 USB to serial adaptor driver The (in my view important) dmesg parts when a adaptor is connected during booting without Legacy USB support enabled: [17179580.048000] usbcore: registered new driver usbserial [17179580.048000] drivers/usb/serial/usb-serial.c: USB Serial support registered for generic [17179580.168000] input: ImPS/2 Logitech Wheel Mouse as /class/input/input2 [17179580.544000] usbcore: registered new driver usbserial_generic [17179580.544000] drivers/usb/serial/usb-serial.c: USB Serial Driver core [17179580.616000] drivers/usb/serial/usb-serial.c: USB Serial support registered for pl2303 [17179580.800000] usb 2-1: new low speed USB device using ohci_hcd and address 2 [17179580.960000] usb 2-1: configuration #1 chosen from 1 choice [17179580.964000] usbcore: registered new driver pl2303 [17179580.964000] drivers/usb/serial/pl2303.c: Prolific PL2303 USB to serial adaptor driver [17179581.220000] usb 1-2: new full speed USB device using ohci_hcd and address 3 [17179581.372000] usb 1-2: configuration #1 chosen from 1 choice [17179581.376000] pl2303 1-2:1.0: pl2303 converter detected [17179581.376000] usb 1-2: pl2303 converter now attached to ttyUSB0 [17179581.376000] usbcore: registered new driver hiddev Note that the previous kernel (2.6.15) had some problems with my laptop too. I needed irqpoll as boot parameter otherwise USB did not work at all. The current kernel behaves the same regardless whether I use irqpoll or not. Current workaround: Disconnect the adaptor before booting and connect the adaptor later or disable "Legacy USB Support" in the BIOS. Steps to reproduce: Enable "Legacy USB Support" in the BIOS. Connect a serial to USB adaptor and try to boot 2.6.16
Then it sounds like you have a buggy bios (seriously.) Just leave that bios config option off, it's not recommended that you enable it for Linux anyway.