Re: PROBLEM: lsusb -v freezes kernel on Acer ES1-111M

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On Sat, 12 Sep 2015, Roland Weber wrote:

> Hi Alan,
> 
> I'm sending a "Reply to all" on this mail. Should I continue to keep
> Mathias and Bjorn on copy and cross-posting to linux-pci@ (I'm not
> yet subscribed there, so that post probably won't get through anyway)?

Most kernel lists don't require posters to subscribe.  Yes, please keep 
everybody on the CC: list.

> > [Roland, what happens if you try unbinding xhci-hcd before ehci-hcd?  
> > Note that unbinding xhci-hcd will cause your wireless keyboard & mouse
> > to stop working, so you'll have to use a shell script or a network
> > login to run the test.]
> 
> The outcome is the same, the system freezes on the readl.
> See below for the transcript from a screen photo.
> 
> > I say this may be relevant because Roland found that ehci-hcd was
> > unable to communicate over the USB bus if it tried to do so before
> > xhci-hcd was probed.  This happens in the 3.17 or earlier kernel -- and
> > that kernel doesn't suffer the freeze problem.
> 
> I can also produce the freeze on 3.17, with some extra steps:

Okay, that's worth knowing.

> (after boot there's just the ehci-pci bus with no device)
> - unbind ehci-pci
> - bind ehci-pci

During both the unbind and the bind, the debugging lines you added to
ehci-hcd.c should show up.  Do they?

> (now the ehci-pci bus has the missing device)
> - unbind ehci-pci
> 
> So the only reason why the older kernels didn't freeze is that
> the device in question couldn't be initialized with the original
> probe sequence. I'll try your blacklisting tip over the weekend.

I wouldn't call it the "only reason".  Rather, it's another symptom
arising from the same underlying problem.

Alan Stern

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