Re: [RFC PATCH] usb/acpi: Add support usb port power off mechanism for device fixed on the motherboard

Alan Stern
2012-05-11T14:20:32Z

On Fri, 11 May 2012, Peter Stuge wrote:

> Sarah Sharp wrote:
> > Maybe we need an "off" setting that forces the port off?
>
> FWIW this would be very welcome in libusb, to do a hard reset of
> bus-powered devices.
>
> It can be attempted via SET_FEATURE(PORT_POWER) to the hub, but a
> "real" API would be nice.

But remember that such an API would be very unreliable. Many hubs and
root hubs cannot shut off port power at all, and some of the remaining
ones use ganged power switches (you have to turn off all the ports in a
gang before power is removed from any of them).

Alan Stern