On Mon, 23 Apr 2012, Carles Pina i Estany wrote: > Hello, > > On Apr/23/2012, Alan Stern wrote: > > On Mon, 23 Apr 2012, Carles Pina i Estany wrote: > > > > 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 ports. > > :-( > > > 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. > > > > http://marc.info/?l=linux-usb&m=127162615232234&w=2 > > I've done some tests with two results. > > ** The good: > Connecting a USB card reader (without any card inside): > pinux:/home/carles/down# ./hubpower 1:1 status > Port 1 status: 0100 Power-On > Port 2 status: 0501 High-Speed Power-On Connected > Port 3 status: 0100 Power-On > Port 4 status: 0100 Power-On > Port 5 status: 0100 Power-On > Port 6 status: 0100 Power-On > Port 7 status: 0100 Power-On > Port 8 status: 0100 Power-On > pinux:/home/carles/down# > > (if I remove the card reader: the "High-Speed Power-On Connected" > changes to "Power-On") > > pinux:/home/carles/down# ./hubpower 1:1 power 2 off > Port 2 status: 0503 High-Speed Power-On Enabled Connected > > Then the LED of the card reader is off (before was blinking/on all the > time) This doesn't mean the card reader is receiving no power. Probably the port was disabled but the power remained on. > pinux:/home/carles/down# ./hubpower 1:1 bind > Bind-driver request sent to the kernel > > Led is on again :-) > > In 2006 I achieved the same or similar with a mouse. I don't know if the > port had some power in or not, but the led was on/off (wich echo's into > /proc or /sys, I don't know). > > ** The bad: > Then the "bad" part: I tried the same with a USB dumb device. Sadly is > not a fan that I'd know in one moment :-( but it's a USB aroma device. > It's so dumb that connecting it to the same physical USB port and doing > lsusb or ./hubpower 1:1 status is not showing anything (for 2 or 3 > dollars I was expecting it :-) ) > > And doing ./hubpower 1:1 power 2 off is not switching off, in terms that > it doesn't get cold. > > I guess that this is what you expected and not possible to fix software > wise (fans, USB aromas?) Right. > (any cheap but a bit smarter USB aroma device that I could control using > software? Or some easy work around to switch off and on devices like > fans or these things?) Try doing a web search for terms like USB power switching. Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
