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Date: Wed, 13 Jul 2011 11:59:53 -0400 (EDT)
From: Alan Stern <stern@rowland.harvard.edu>
To: Ming Lei <tom.leiming@gmail.com>
cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
	Ming Lei <ming.lei@canonical.com>,
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	Jeremy Kerr <jeremy.kerr@canonical.com>,
	Mauro Carvalho Chehab <mchehab@redhat.com>
Subject: Re: [PATCH] uvcvideo: add fix suspend/resume quirk for Microdia
 camera
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On Wed, 13 Jul 2011, Ming Lei wrote:

> Hi,
> 
> On Wed, Jul 13, 2011 at 11:20 PM, Alan Stern <stern@rowland.harvard.edu> wrote:
> 
> > Why should system suspend be different from runtime suspend?  Have you
> 
> This is also my puzzle, :-)
> 
> > compared usbmon traces for the two types of suspend?
> 
> Almost same.

Come on.  "Almost same" means they are different.  That difference is
clearly the important thing you need to track down.

>  If I add USB_QUIRK_RESET_RESUME quirk for the device,
> the stream data will not be received from the device in runtime pm case,
> same with that in system suspend.

uvcvideo should be able to reinitialize the device so that it works
correctly following a reset.  If the device doesn't work then uvcvideo
has a bug in its reset_resume handler.

> Maybe buggy BIOS makes root hub send reset signal to the device during
> system suspend time, not sure...

That's entirely possible.

Alan Stern