linux-kernel - Re: [34-stable regression] USB delay init quirk causes device events loss

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Date:	Mon, 13 Sep 2010 11:37:49 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Jiri Slaby <jslaby@...e.cz>
cc:	phil@...m.com, <stable@...nel.org>, Greg KH <gregkh@...e.de>,
	USB list <linux-usb@...r.kernel.org>,
	Linux kernel mailing list <linux-kernel@...r.kernel.org>
Subject: Re: [34-stable regression] USB delay init quirk causes device events
 loss

On Mon, 13 Sep 2010, Jiri Slaby wrote:

> On 09/13/2010 04:48 PM, Alan Stern wrote:
> > On Mon, 13 Sep 2010, Jiri Slaby wrote:
> >> In other words, what I could do is to add some printks into
> >> hub_port_connect_change if that's called at all. If you need some
> >> thorough debugging printks, please send me a patch to test instead.
> > 
> > Hmm.  I'd prefer to explain how it's all supposed to work and let you
> > figure out where best to look.  Or try to debug it myself.  Does this
> > happen with other sorts of USB devices as well, or just wacom?
> 
> With some sort of devices (I cannot reproduce myself). It's unrelated to
> wacom -- people with wacom were unable to even start X with this kernel.
> If you look at the bugreport, there are several examples:
> ID 046d:c517 Logitech, Inc. LX710 Cordless Desktop Laser defunct
> Microsoft USB keyboard defunct x Logitech mice OK
> 046a:0021 Cherry GmbH keyboard defunct
> logitech wireless laptop mouse defunct
> A$Tech wireless laptop mouse defunct
> TypeMatrix USB 2030 (ID : 1e54:2030) defunct

Okay, I see the problem.  By moving usb_detect_quirks earlier, we end 
up calling usb_disable_autosuspend too soon -- before the 
pm_runtime_enable call in usb_new_device.  In 2.6.35 this doesn't 
matter because the implementation of usb_autosuspend_device has 
changed.

So yes, in the end it looks like the best course is to revert this
patch from 2.6.34.stable.  This is unfortunate but I don't see any way
around it without making changes that aren't present in the current
kernel. For example, the pm_runtime_set_active and pm_runtime_enable
calls could also be moved from usb_new_device into
hub_port_connect_change.

Alan Stern

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