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Date:   Thu, 23 Jan 2020 10:50:05 -0500 (EST)
From:   Alan Stern <stern@rowland.harvard.edu>
To:     Paul Zimmerman <pauldzim@gmail.com>
cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        David Heinzelmann <heinzelmann.david@gmail.com>,
        <linux-kernel@vger.kernel.org>, <linux-usb@vger.kernel.org>
Subject: Re: [REGRESSION][BISECTED] 5.5-rc suspend/resume failure caused by
 patch a4f55d8b8c14 ("usb: hub: Check device descriptor before resusciation")
In-Reply-To: <20200122165454.757aaa25@EliteBook>
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On Wed, 22 Jan 2020, Paul Zimmerman wrote:

> > Still, since there was no real connection change at the port, there's
> > no reason to call hub_port_connect_change() here.  Let's see if the
> > patch below fixes your problem.
> > 
> > Alan Stern
> > 
> > 
> > 
> > Index: usb-devel/drivers/usb/core/hub.c
> > ===================================================================
> > --- usb-devel.orig/drivers/usb/core/hub.c
> > +++ usb-devel/drivers/usb/core/hub.c
> > @@ -1216,11 +1216,6 @@ static void hub_activate(struct usb_hub
> >  #ifdef CONFIG_PM
> >  			udev->reset_resume = 1;
> >  #endif
> > -			/* Don't set the change_bits when the device
> > -			 * was powered off.
> > -			 */
> > -			if (test_bit(port1, hub->power_bits))
> > -				set_bit(port1, hub->change_bits);
> >  
> >  		} else {
> >  			/* The power session is gone; tell hub_wq */
> > 
> 
> I can confirm this fixes the issue for me, I did a couple dozen
> suspend/resume cycles without seeing a failure.
> 
> I see the code you removed was added by Lan Tianyu in commit
> ad493e5e5805 ("usb: add usb port auto power off mechanism"). I

No, not really.  The set_bit() call was added by me in a much earlier
commit (8808f00c7adf, merged in 2008).  Lan Tianyu merely added the
"if" test, so that set_bit() doesn't always get called.  Now with this
change, set_bit() never gets called.

> wonder if your patch would break that? I don't know what that is
> or how to test it.

While some code review by people who are familiar with this material 
wouldn't hurt, I don't think you need to worry about any additional 
testing.

> In any case:
> Tested-by: Paul Zimmerman <pauldzim@gmail.com>

Thank you.  I'll submit the patch soon.

Alan Stern