Re: Power off USB port

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On Mon, 23 Apr 2012, Carles Pina i Estany wrote:

> Hi,
> Short version:
> Is it possible to "switch off" a USB port? (even the minimum standard
> power)

Short answer: No.

> I've been Googling and I haven't been able to resolve my problem:
> I'm using Kernel 3.2.0 (from Debian) and I'd like to switch off a USB
> port. The use case is that I have a dumb device (for example a fan)
> which one doesn't identify to the system (lsusb, dmesg, etc. says
> nothing) and I'd like to be able to switch off and on it.
> I've tried a variety of things to
> /sys/bus/usb/devices/usb2|2-2.../power/level and power/control, but my
> understanding is that it changed in the last kernels, and seems that now
> is not possible to do. Am I trying the impossible?
> Any workaround in the kernel / user level side?

No workarounds.  The circuitry in the USB hardware commonly used in
desktop and laptop computers is not capable of turning off power to USB

The same is true of many hubs.  There are some hubs which _can_ turn 
off power to ports, but relatively few brands support this.  I don't 
know which ones do.

Here is a link to a program which attempts to turn turn port power on 
and off.  You can at least use it for testing.

> In case that it matters:
> 00:1d.0 USB controller: Intel Corporation N10/ICH 7 Family USB UHCI
> Controller #1 (rev 02)
> I think that I did it back to the 2006 playing with powertop and
> different things.
> Regards and many thanks!

You're welcome.

Alan Stern

> PS: if this is off-topic feel free to contact me off-the-list / send me
> to a better mailing list -I haven't found

This is right on-topic.

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