Linux USB: turning the power on and off?

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 fileto change the device's setting."on" means that the device should be resumed andautosuspend is not allowed.  (Of course, systemsuspends are still allowed.)"auto" is the normal state in which the kernel isallowed to autosuspend and autoresume the device."suspend" means that the device should remainsuspended, and autoresume is not allowed.  (But remotewakeup may still be allowed, since it is controlledseparately 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!

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/unbindsleep 1echo '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.

You could use my tool uhubctl - command line utility to control USB power per port for compatible USB hubs.

It works only on hubs that support per-port power switching, but note that many modern motherboards have USB hubs that support this feature. Also, last version of uhubctl supports USB 3.0 hubs, and good news is that quite a few new USB 3.0 hubs are supporting this feature.

To compile:

git clone https://github.com/mvp/uhubctlcd uhubctlmake

To install system wide as /usr/sbin/uhubctl:

sudo make install

To list status of all hubs and ports that can be controlled by uhubctl:

uhubctl

To turn off power on port 5 of single compatible hub:

uhubctl -a 0 -p 5

To toggle power off then on:

uhubctl -a 2 -p 5

Read more here.