Re: USB Hub Port Power Control and Hotplug Events

[Greg KH <greg@kroah.com>]

On Fri, Aug 11, 2006 at 09:39:47AM +0200, Guennadi Liakhovetski wrote:
> On Thu, 10 Aug 2006, Andy Dalton wrote:
> 
> > While experimenting, I noticed something a bit strange.  If I power
> > down a port on the USB hub, then later power it back on,  I do *not*
> > get a hotplug removal event on power off, but I *do* get an insertion
> > event on power on.
> 
> It has been discussed on the USB-devel list. The thing is - the hub 
> doesn't report a "port status change" on "port power off". It's on power 
> on it first reports a "disconnect" and then immediately a "new device". 
> And the system cannot really simulate this event for you because the "port 
> power off" command can come from various places - kernel drivers, user 
> space. So, your only option seems to be to use the fact that it's you who 
> issues the command, so, you know that the device is gone. Just use this 
> knowledge.
> 
> Not sure, but I don't think you can tell the kernel that the device is 
> gone...

No, the USB stack does not allow you to do this at this point in time,
sorry.

You can unbind a device from a driver though, that would prevent it from
being used by any userspace programs.

thanks,

greg k-h

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