Re: USB device not found on boot, only on insertion

[Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>]

On Fri, 3 Jul 2009, David Brownell wrote:

> On Friday 03 July 2009, Pierre Ossman wrote:
> > Is there any way I can force
> > the bus to power down and up again to simulate removal and reinsertion?
> 
> As Alan noted -- not really.  Maybe hook it up to an external
> hub; most of those seem to claim they support power switching.
> 
> I did once have a system with an OHCI root hub which supported
> power switching.  Which was handy because one UPS needed to
> start its enumeration from link-power-off, not unlike what you
> are observing.
> 
> That system made a good regression test for the feature in the
> Linux-USB stack whereby it tried to force root hub enumeration
> to start from power-off.  Since that system died a while back
> (sigh), I no longer know if that still works on those fortunate
> systems which *do* support such switching.

If you have any external hubs that support port-power switching, they
should make equally good test cases.  After all, Linux doesn't make 
much distinction between root hub and external hub enumeration.

Alan Stern

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