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

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Message-ID: <20131114233055.GR10371@xanatos>
Date:	Thu, 14 Nov 2013 15:30:55 -0800
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>,
	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>,
	"Alexis R. Cortes" <alexis.cortes@...com>
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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