linux-kernel - Re: [PATCH v2] usb: core: don't try to reset_device() a port that got just disconnected

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Date:	Wed, 31 Jul 2013 09:48:49 -0700
From:	Sarah Sharp <sarah.a.sharp@...ux.intel.com>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Julius Werner <jwerner@...omium.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
	Vincent Palatin <vpalatin@...omium.org>,
	Benson Leung <bleung@...omium.org>
Subject: Re: [PATCH v2] usb: core: don't try to reset_device() a port that
 got just disconnected

On Wed, Jul 31, 2013 at 10:43:30AM -0400, Alan Stern wrote:
> On Tue, 30 Jul 2013, Julius Werner wrote:
> 
> > The USB hub driver's event handler contains a check to catch SuperSpeed
> > devices that transitioned into the SS.Inactive state and tries to fix
> > them with a reset. It decides whether to do a plain hub port reset or
> > call the usb_reset_device() function based on whether there was a device
> > attached to the port.
> > 
> > However, there are device/hub combinations (found with a JetFlash
> > Transcend mass storage stick (8564:1000) on the root hub of an Intel
> > LynxPoint PCH) which can transition to the SS.Inactive state on
> > disconnect (and stay there long enough for the host to notice). In this
> > case, above-mentioned reset check will call usb_reset_device() on the
> > stale device data structure. The kernel will send pointless LPM control
> > messages to the no longer connected device address and can even cause
> > several 5 second khubd stalls on some (buggy?) host controllers, before
> > finally accepting the device's fate amongst a flurry of error messages.
> > 
> > This patch makes the choice of reset dependent on the port status that
> > has just been read from the hub in addition to the existence of an
> > in-kernel data structure for the device, and only proceeds with the more
> > extensive reset if both are valid.
> > 
> > Signed-off-by: Julius Werner <jwerner@...omium.org>
> This version looks better.
> 
> Acked-by: Alan Stern <stern@...land.harvard.edu>

Thanks Alan, I'll send this off to Greg shortly.

Sarah Sharp
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