linux-kernel - RE: [PATCH] usb: hub: Use correct reset for wedged USB3 devices that are NOTATTACHED

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Date:	Tue, 19 Nov 2013 14:53:22 +0000
From:	"Cortes, Alexis" <alexis.cortes@...com>
To:	Sarah Sharp <sarah.a.sharp@...ux.intel.com>,
	Alan Stern <stern@...land.harvard.edu>
CC:	Julius Werner <jwerner@...omium.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	Benson Leung <bleung@...omium.org>,
	Vincent Palatin <vpalatin@...omium.org>
Subject: RE: [PATCH] usb: hub: Use correct reset for wedged USB3 devices
 that are NOTATTACHED

Hi Sarah,

Sorry for my delayed response, I just saw your e-mail (it got filtered somehow). About your question: actually I'm not sure, I'll have to check that to confirm it. I'll get back to you with an answer as soon as I have it.

Best Regards,
Alexis Cortes.

-----Original Message-----
From: Sarah Sharp [mailto:sarah.a.sharp@...ux.intel.com] 
Sent: Thursday, November 14, 2013 5:31 PM
To: Alan Stern
Cc: Julius Werner; Greg Kroah-Hartman; LKML; linux-usb@...r.kernel.org; Benson Leung; Vincent Palatin; Cortes, Alexis
Subject: Re: [PATCH] usb: hub: Use correct reset for wedged USB3 devices that are NOTATTACHED

On Thu, Nov 07, 2013 at 10:32:33AM -0500, Alan Stern wrote:
> On Wed, 6 Nov 2013, Julius Werner wrote:
> 
> > > What if the device is in USB_STATE_SUSPENDED?
> > 
> > I'm not sure that is possible at that point in hub_events(), I don't 
> > know of a way that could lead to this situation. I could still add 
> > the check just to be sure if you want it, though.
> 
> I don't know either.  But Sarah has said that ports can spontaneously 
> go into Compliance Mode for no apparent reason.  If that can happen, 
> maybe it can happen while the port is in U3 and the device is 
> suspended.  In such cases, though, you'd need to do a reset-resume 
> rather than a simple reset.

Looking at commits c3897aa5386faba77e5bbdf94902a1658d3a5b11 and 71c731a296f1b08a3724bd1b514b64f1bda87a23, it seems that the TI host controllers' ports can go into compliance mode only when a device is inserted.  Once the device is link trained by the redriver, the port shouldn't go into compliance mode.  So we should never see compliance mode on a port with an attached USB device in suspend.

Alex, can you confirm that the TI host's port won't go into compliance mode while a connected device is suspended?

> > > Not at all.  If a device is unplugged, its state changes to 
> > > NOTATTACHED before the driver is unbound.  During that time, the 
> > > driver will see all its URBs failing, so it may very well try to reset the device.
> > > (For example, usbhid behaves like this.)  That isn't a bug.
> > 
> > Oh, okay, I wasn't quite sure how that plays together. Would you 
> > think it's still valuable to print it out (maybe as dev_info() 
> > instead of
> > dev_warn()) instead of just silently ignoring the reset request? It 
> > would have certainly been useful for me to find this problem faster, 
> > but I can take it out again if you think it would result in too much 
> > noise.
> 
> I think keeping dev_dbg() is best.  If you're searching for the 
> solution to a problem, you should have debugging enabled and so you 
> ought to see the message.
> 
> Alan Stern
> 
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