linux-kernel - Re: [linux-usb-devel] [PATCH] : Allow embedded developers USB options normally reserved for OTG

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Message-ID: <Pine.LNX.4.44L0.0801021556070.2990-100000@iolanthe.rowland.org>
Date:	Wed, 2 Jan 2008 15:58:38 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	David Brownell <david-b@...bell.net>
cc:	Mike Frysinger <vapier.adi@...il.com>, <gregkh@...e.de>,
	<linux-usb-devel@...ts.sourceforge.net>,
	Robin Getz <rgetz@...ckfin.uclinux.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [linux-usb-devel] [PATCH] : Allow embedded developers USB options
 normally reserved for OTG

On Wed, 2 Jan 2008, David Brownell wrote:

> On Wednesday 02 January 2008, Alan Stern wrote:
> > On Wed, 2 Jan 2008, Mike Frysinger wrote:
> > 
> > > perhaps the code size is arguable as to whether it really matters.
> > > the reason we want it is that we have a USB host controller that will
> > > not work with USB hubs, so we want to make sure the system does not
> > > attempt such things.  (yes, such a USB host controller is retarded,
> > > but the decision was out of our hands.)
> > 
> > Just out of curiosity, how does a host controller manage to avoid
> > working with external hubs? 
> 
> The transaction translators in external high speed hubs require
> hosts to issue particular USB transactions.  If the host controller
> doesn't implement the that split transaction support, then it won't
> be supporting external hubs.

So in theory one could connect a high-speed hub to such a host
controller and expect it to communicate with high-speed devices.  So
long as no full- or low-speed devices are added there wouldn't be any
split transactions.  It wouldn't be USB-2.0 compliant but it should
still work.

Alan Stern

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