I tried to use echo -n '2-2' > /sys/bus/usb/drivers/usb/unbind to unbind a USB device that connects to FTDI chip, but I found that it get auto binded right after I run the command.
My lsusb -t looks like:
/: Bus 02.Port 1: Dev 1, Class=root_hub, Driver=xhci_hcd/4p, 5000M
|__ Port 2: Dev 6, If 0, Class=Vendor Specific Class, Driver=usbfs, 5000M
|__ Port 2: Dev 6, If 1, Class=Vendor Specific Class, Driver=usbfs, 5000M
/: Bus 01.Port 1: Dev 1, Class=root_hub, Driver=xhci_hcd/10p, 480M
My lsusb looks like:
Bus 002 Device 006: ID 0403:**** Future Technology Devices International, Ltd
Bus 002 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
ls /sys/bus/usb/devices has:
1-0:1.0 2-0:1.0 2-2 2-2:1.0 2-2:1.1 usb1 usb2
After I run sudo bash -c 'echo "2-2" > unbind', my dmesg outputs following new messages
[Jan15 11:03] usb 2-2: USB disconnect, device number 3
[ +0.272120] usb 2-2: new SuperSpeed USB device number 4 using xhci_hcd
[ +0.020880] usb 2-2: New USB device found, idVendor=0403, idProduct=***
[ +0.000006] usb 2-2: New USB device strings: Mfr=1, Product=2, SerialNumber=3
[ +0.000003] usb 2-2: Product: FTDI **********
[ +0.000003] usb 2-2: Manufacturer: FTDI
[ +0.000002] usb 2-2: SerialNumber: 000000000001
You can see that USB is disconnected, but then new USB is found and get assigned a new device number. It feels like my USB device is rebinded instead of unbind. Does anyone know the reason? Thanks!
More information: I tried run echo -n usb2 > /sys/bus/usb/drivers/usb/unbind to unbind bus 2, it works and dmesg shows:
[Jan15 12:33] usb 2-2: USB disconnect, device number 8
My ls /sys/bus/usb/devices changed to:
1-0:1.0 usb1 usb2
which I feel incorrect. From my understand 2-0:1.0 should alaways be there? Then I tried to add bus2 back by echo -n usb2 > /sys/bus/usb/drivers/usb/bind, I got error in dmesg
[Jan15 12:48] usb usb2: can't set config #1, error -22