Re: So, what's the status on the recent patches here?

[Alan Stern <stern@rowland.harvard.edu>]

On Fri, 25 Aug 2006, Woodruff, Richard wrote:

> > > > ?  Wouldn't suspending the entire bus completely stop the
> throughput
> > > of
> > > > any attached device?
> > >
> > > Not necessarily (right?).  If I shut off VBUS then yes then I need
> to
> > > re-enumerate for sure.  One might figure out a cleaver way of
> shutting
> > > it off and turning it back on in between host requests.
> > 
> > No, you can't do that.  Without VBUS power there's no reliable way to
> > detect disconnects or media changes.
> 
> That's a good point.  I wonder in this case if it is possible to keep a
> list of what was there.  When you re-power if its not there, it should
> be like it was disconnected, then act accordingly.  If it is there all
> is ok.  It seems unlikely that the same PID/VID device would have
> replaced it.  New devices would show up as not being there before.
> 
> Coding that all up would likely be a bunch of work assuming it was
> possible.

There have been long discussions about this in the past, mainly focused on 
suspend-to-disk (which generally turns off all power to the USB 
controllers).  They were pretty much inconclusive; it's safe to assume no 
progress will be made on supporting this for a long time, if ever.

Note that you don't need to replace one device with another having the 
same PID/VID.  It could be the very same device but with new media loaded.  
That would be just as bad.

Alan Stern