linux-kernel - Re: [linux-pm] wacom + runtime PM = AA deadlock

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Message-Id: <201009141603.59338.oneukum@suse.de>
Date:	Tue, 14 Sep 2010 16:03:59 +0200
From:	Oliver Neukum <oneukum@...e.de>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Jiri Slaby <jslaby@...e.cz>, Dmitry Torokhov <dtor@...l.ru>,
	pingc@...om.com, "linux-pm" <linux-pm@...ts.linux-foundation.org>,
	Linux kernel mailing list <linux-kernel@...r.kernel.org>,
	linux-input@...r.kernel.org
Subject: Re: [linux-pm] wacom + runtime PM = AA deadlock

Am Dienstag, 14. September 2010, 16:01:14 schrieb Alan Stern:
> On Tue, 14 Sep 2010, Oliver Neukum wrote:
> 
> > Am Montag, 13. September 2010, 22:02:16 schrieb Alan Stern:
> > > > > Is there any point in resuming the device during close() just in order
> > > > > to kill the interrupt URB?  It seems counterproductive -- if the device 
> > > > > had been suspended then there wouldn't be any interrupt URB to kill in 
> > > > > the first place.
> > > > 
> > > > Suppose the device does not support remote wakeup. It would never
> > > > be autosuspended while it is open, but simply resetting the flag
> > > > would never reach the PM layer.
> > > 
> > > Whoops, that's right.  I didn't see the assignment to 
> > > needs_remote_wakeup.
> > 
> > Should I have used usb_autopm_get_interface_no_resume()?
> 
> That actually would work.  It's a good idea.  The only drawback (not a
> big one) is that if the device _was_ suspended with remote wakeup
> enabled, doing this wouldn't turn off remote wakeup.  I think that
> doesn't matter.

I am afraid it does matter as devices whose remote wakeup is enabled
may draw more power.

	Regards
		Oliver
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