Re: Strange behavior of high-speed hub during hibernation test

On Tuesday 11 December 2007, Alan Stern wrote:
> Dave:
> 
> I just tried doing some hibernation testing, and my external high-speed
> hub is behaving very strangely.  The test is simple.  First plug in the
> hub, then plug a flash drive into the hub to keep it from
> autosuspending.  Then:
> 
> 	echo test >/sys/power/disk
> 	echo disk >/sys/power/state
> 
> The first line causes the hibernation to stop after the PM_EVENT_FREEZE 
> message has been sent; after that everything is woken back up.  There 
> are no bus-power-level changes since the EHCI controller remains in D0 
> throughout.
> 
> This sequence causes the hub to disconnect and reconnect itself!  When
> khubd starts running again, it sees the port-connect-change event.
> 
> This happens only with the hub; if I plug the flash drive into the 
> computer's USB port instead of plugging the hub there, the drive 
> remains connected at the end of the test.
> 
> The hub doesn't disconnect itself like this during a runtime suspend.  
> In fact, if I run the hibernation test while the hub is already
> suspended then there is no port-connect-change event and the hub can be
> resumed normally.
> 
> Do you have any idea how this could be happening?  As far as I can 
> tell, the hub shouldn't be able to distinguish one sort of suspend from 
> another.

This doesn't ring any bells with me.  It seems buglike.  :)

- Dave


> 
> Alan Stern
> 


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