How to enable/power off a port

How to enable/power off a port

[rasmit.ranjan]

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Hi all,
	I can suspend a port from the user space manualy by doing
	
	echo -n 3 > /sys/bus/usb....../power/state

Similarlly can I enable/power off a port from the user space manually ?

Please suggest.

Thanks and regards,
Rasmit Ranjan Swain.


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Re: How to enable/power off a port

[Greg KH]

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On Mon, Apr 17, 2006 at 05:12:11PM +0530, rasmit.ranjan@wipro.com wrote:
> Hi all,
> 	I can suspend a port from the user space manualy by doing
> 	
> 	echo -n 3 > /sys/bus/usb....../power/state
> 
> Similarlly can I enable/power off a port from the user space manually ?

Search the archives of the linux-usb-devel mailing list for a small
program that does this through usbfs.  That's the only way to disable
power for a USB port (and then only for some hubs, not all support it.)

good luck,

greg k-h

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Re: How to enable/power off a port

[Alan Stern]

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On Mon, 17 Apr 2006 rasmit.ranjan@wipro.com wrote:

> Hi all,
> 	I can suspend a port from the user space manualy by doing
> 	
> 	echo -n 3 > /sys/bus/usb....../power/state
> 
> Similarlly can I enable/power off a port from the user space manually ?

It depends on where the port is.  For ports built into the computer, the 
answer is generally No.  The USB controller hardware in computers does not 
have per-port power control.

On some systems you might be able to turn off power to _all_ the ports
attached to a particular USB host controller by turning off power to the
controller itself (put it in a D3cold state).  But this would affect more
than one port, and most systems won't allow you to do it anyway.

If the port is part of an external hub instead of build into the computer, 
you may be able to do it.  Many hubs do not support per-port power 
control, but some of them do.  You can get more information and a 
userspace program here:

http://www.gniibe.org/ac-power-by-usb/ac-power-control.html

Alan Stern


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