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

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Message-ID: <001b01c84e2a$60558730$21009590$@com>
Date:	Thu, 3 Jan 2008 22:31:54 +0530
From:	"Richard D" <richard@...unus.com>
To:	"'Alan Stern'" <stern@...land.harvard.edu>,
	"'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

> -----Original Message-----
> From: linux-kernel-owner@...r.kernel.org [mailto:linux-kernel-
> owner@...r.kernel.org] On Behalf Of Alan Stern
> Sent: Thursday, January 03, 2008 2:29 AM
> To: David Brownell
> Cc: Mike Frysinger; gregkh@...e.de; linux-usb-
> devel@...ts.sourceforge.net; Robin Getz; 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.


Perhaps we could reject any low/full speed devices after the USBV
enumeration phase itself. This would need perhaps a flag in the struct
hc_driver which the hub code (that does the enumeration) can check and
reject further enumeration?
Atleast this way we can support high speed devices.



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