Linux USB: turning the power on and off?
The usbfs interaction seems to have changed a number of times since this question was originally answered. So, here's how I cycle hub port power on Ubuntu Oneiric Ocelot from a Bash shell.
Search for the bus and device number:
sudo lsusb -v|less
Locate the device in the bus / hub port hierarchy using the bus and device number:
sudo lsusb -t|less
The syntax seems to be 'bus-port.port.port.port.port...' For example, my mouse is connected to an external hub which connects to my computer's hub which internally connects to a root hub:
/: Bus 02.Port 1: Dev 1, Class=root_hub, Driver=ehci_hcd/2p, 480M
|__ Port 1: Dev 2, If 0, Class=hub, Driver=hub/6p, 480M
|__ Port 1: Dev 3, If 0, Class=hub, Driver=hub/3p, 480M
|__ Port 1: Dev 6, If 0, Class=HID, Driver=usbhid, 1.5M
So, '2-1.1.1' in the above case. Finally, cycle the port power:
echo '2-1.1.1'|sudo tee /sys/bus/usb/drivers/usb/unbind
sleep 1
echo '2-1.1.1'|sudo tee /sys/bus/usb/drivers/usb/bind
I haven't hooked up a protocol analyzer to see what's actually happening on the bus, but I know my mouse light turns off when I unbind it. I'm guessing at a lower layer this is interacting with the EHCI host controller to actually shut power off on the port. This is particularly useful for embedded devices, such as a UVC webcams, which never seem to function properly and would otherwise require a system reboot to reset.
See also the udevadm
command.
There is a sys entry for this in Linux. From Documentation/usb/power-management.txt:
power/level
This file contains one of three words: "on", "auto", or "suspend". You can write those words to the file to change the device's setting. "on" means that the device should be resumed and autosuspend is not allowed. (Of course, system suspends are still allowed.) "auto" is the normal state in which the kernel is allowed to autosuspend and autoresume the device. "suspend" means that the device should remain suspended, and autoresume is not allowed. (But remote wakeup may still be allowed, since it is controlled separately by the power/wakeup attribute.)
Something like: echo on > /sys/bus/usb/devices/usb5/power/level
You may need to play with the autosuspend setting as well. Without telling the kernel to stop trying, it may suspend the port automatically.
Good luck!