Re: [PATCH] USB: hub: Don't record a connect-change event during reset-resume

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

On Fri, 31 Jan 2020, Paul Zimmerman wrote:

> > Note that performing the unnecessary check is not actually a bug.
> > Devices are supposed to be able to send descriptors back to the host
> > even when they are busy doing something else.  The underlying cause of
> > Paul's problem lies in his Bluetooth adapter.  Nevertheless, we
> > shouldn't perform the same check twice in a row -- and as a nice side
> > benefit, removing the extra check allows the Bluetooth adapter to work
> > more reliably.
> 
> Actually, at the time the failure happens, the bluetooth driver is putting
> the device into a "manufacturer mode" and downloading a firmware patch to
> the device. So I don't think we can fault the device for not responding to
> a get-descriptor request at that point. Probably there should be some kind
> of locking in the driver while that is being done.

Heh.  We don't have any locking of that sort in the kernel.  Any user 
at any time can run "lsusb -v" and that program will try to communicate 
with every attached USB device.  There's no way to claim exclusive 
rights to a device.

The fact that firmware loading works at all is more or less a matter of
luck (although the odds are with us).

> Nevertheless, your patch makes everything work again, so I think it's
> "good enough" :)
> 
> Thanks,
> Paul

You're welcome.

Alan Stern