linux-kernel - Re: [PATCH v7 10/14] usb: otg: add hcd companion support

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Date:	Wed, 11 May 2016 10:47:20 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Roger Quadros <rogerq@...com>
cc:	Rob Herring <robh@...nel.org>, <yoshihiro.shimoda.uh@...esas.com>,
	<peter.chen@...escale.com>, <balbi@...nel.org>,
	<gregkh@...uxfoundation.org>, <dan.j.williams@...el.com>,
	<jun.li@...escale.com>, <mathias.nyman@...ux.intel.com>,
	<tony@...mide.com>, <Joao.Pinto@...opsys.com>,
	<abrestic@...omium.org>, <linux-usb@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <linux-omap@...r.kernel.org>,
	<devicetree@...r.kernel.org>
Subject: Re: [PATCH v7 10/14] usb: otg: add hcd companion support

On Wed, 11 May 2016, Roger Quadros wrote:

> > What I mean is if you have 2 EHCI controllers with 2 companion 
> > controllers, don't you need to know which companion goes with which EHCI 
> > controller? Just like you do for the otg-controller property.
> > 
> 
> That is a very good point. I'm not very sure and it seems that current code won't work
> with multiple EHCI + companion instances.
> 
> Alan, does USB core even know which EHCI and OHCI are linked to the same port
> or the handoff is software transparent?

The core knows.  It doesn't use the information for a whole lot of 
things, but it does use it in a couple of places.  Search for 
"companion" in core/hcd-pci.c and you'll see.

Alan Stern