usb/80829: possible panic when loading USB-modules

[Warner Losh]

> I'm planning to use the stack method and have usbd_probe_and_attach() called 
> again from uhub_explore() via a call similar to usb_explore(). Leaving 
> devices after usbd_probe_and_attach() has returned, will _not_ work, except 
> for generic or specific USB drivers. It will not work for "ums", "ukbd" and 
> so on, because a device can have more than one configuration, and it is not 
> sure that the right configuration index is set when usbd_probe_and_attach() 
> returns after the generic probe. Have a look at this (almost finished):
> 
> Implement a new state-variable "udev->probed" and a refcount in "usbd_port" to 
> limit the calling of "usbd_probe_and_attach()".
> 
> Any comments?

I see why you are doing the reference count...  I also see some of the
problems involved.  The main reason that I went from the stack method
to the other method was so that the driver_added stuff would still
work.  That's the goal.  Part of the problem is that the NetBSD device
model ill fits newbus, for reasons that you're discovering...

Warner