Re: Power off USB port

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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)

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?)

(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?)

-- 
Carles Pina i Estany
	http://pinux.info
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