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From: Paul Brook <paul@codesourcery.com>
Subject: Re: [Qemu-devel] [patch 0/2] USB UHCI global suspend / remote wakeup
Date: Fri, 26 Nov 2010 12:09:47 +0000
References: <20101125170439.548474575@redhat.com>
	<20101126021512.GA18020@amt.cnet> <4CEF74B1.1030908@redhat.com>
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To: Gerd Hoffmann <kraxel@redhat.com>
Cc: Matthew Garrett <mjg59@srcf.ucam.org>, kvm <kvm@vger.kernel.org>, Marcelo Tosatti <mtosatti@redhat.com>, qemu-devel@nongnu.org, Glauber de Oliveira Costa <gcosta@redhat.com>, Adam Jackson <ajax@redhat.com>

> On 11/26/10 03:15, Marcelo Tosatti wrote:
> > On Fri, Nov 26, 2010 at 12:38:28AM +0000, Paul Brook wrote:
> >>> This patch enables USB UHCI global suspend/resume feature. The OS will
> >>> stop the HC once all ports are suspended. If there is activity on the
> >>> port(s), an interrupt signalling remote wakeup will be triggered.
> >> 
> >> I'm pretty sure this is wrong.  Suspend/resume works based on physical
> >> topology, i.e. the resume notification should go to the the port/hub to
> >> which the device is connected, not directly to the host controller.
> > 
> > You are correct in that USB HUB emulation does not propagate resume, but
> > this does not make this patch incorrect.
> 
> Well, it does.  When the notification is port based our software model
> should better reflect that, so we have the chance to add resume
> propagation to the hub emulation later on.

Exactly. The patch assumes the device is connected to a root hub port. This 
assumption is incorrect.

The device should be sending the resume signal to the port/hub to which it is 
connected. If that hub is still active it will reactivate the port, and flag a 
port change notification in the normal manner. If the hub is also suspended it 
will propagate the resume notification upstream (which may or may not be the 
root hub).

Paul