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

Alan Stern
2006-08-25T21:42:20Z

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