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

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Date:	Wed, 31 Jul 2013 09:05:43 -0700
From:	Sarah Sharp <sarah.a.sharp@...ux.intel.com>
To:	Julius Werner <jwerner@...omium.org>
Cc:	Alan Stern <stern@...land.harvard.edu>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	LKML <linux-kernel@...r.kernel.org>, linux-usb@...r.kernel.org,
	Vincent Palatin <vpalatin@...omium.org>,
	Benson Leung <bleung@...omium.org>
Subject: Re: [PATCH] usb: core: don't try to reset_device() a port that got
 just disconnected

On Tue, Jul 30, 2013 at 07:33:46PM -0700, Julius Werner wrote:
> > Wait a moment.  Why does each of these attempts lead to a 5-second
> > timeout?  Why don't they fail immediately?
> 
> Now that you mention it, that's a very good question. The kernel
> enqueues a control transfer to the now disconnected address because
> it's internal bookkeeping is not yet updated, but I guess that should
> usually fail very fast from an xHC-internal transaction timeout. I
> have now tried to debug the cause of this: I see the transfer being
> enqueued and the doorbell triggered, but never get a transfer event
> back from it (until the software timeout calls usb_kill_urb() which
> stops the endpoint). With the same setup on a PantherPoint system I
> get the same U1/U2 disable control messages on unplugging, but they
> fail within <5ms with a transaction error... so I guess this must be a
> LynxPoint hardware bug.
> 
> Regardless, calling usb_reset_device() is still wrong and will at
> least lead to pointless transfer attempts and error messages, so I
> think my patch still has merit.

Hmm, 5 seconds is the xHCI command timeout.  Could the driver be
possibly issuing either a Reset Device or Address Device command that
simply times out?

Sarah Sharp
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