Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755888AbYACDwj (ORCPT ); Wed, 2 Jan 2008 22:52:39 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754150AbYACDwa (ORCPT ); Wed, 2 Jan 2008 22:52:30 -0500 Received: from py-out-1112.google.com ([64.233.166.180]:4085 "EHLO py-out-1112.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754253AbYACDw3 (ORCPT ); Wed, 2 Jan 2008 22:52:29 -0500 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=message-id:date:from:to:subject:cc:in-reply-to:mime-version:content-type:content-transfer-encoding:content-disposition:references; b=cKY1nV5l6WCUHLdw42UaXSnzhjJC7LkCUJP24CJvrCB/3hglV/NxEbClEU/N902rWqx1Fk3pQuSGJOahIZZsaTQUuOxETNaVov/sl1khY5lNHrg2t2g5A/oQSlms1MGJBOLXAHrHgxPputXA1W/2po/yxkfH2RsHcpiywhttY+E= Message-ID: <386072610801021952t710db0f8pa2b435224d6926b@mail.gmail.com> Date: Thu, 3 Jan 2008 11:52:27 +0800 From: "Bryan Wu" To: "Alan Stern" Subject: Re: [linux-usb-devel] [PATCH] : Allow embedded developers USB options normally reserved for OTG Cc: "David Brownell" , "Mike Frysinger" , gregkh@suse.de, linux-usb-devel@lists.sourceforge.net, "Robin Getz" , linux-kernel@vger.kernel.org In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Content-Disposition: inline References: <200801021225.28370.david-b@pacbell.net> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1860 Lines: 41 On Jan 3, 2008 4:58 AM, Alan Stern wrote: > 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. > Hmmm, basically, I think the answer is yes. But when you tell customers your devices support USB 2.0, they will try to plug-in lots of USB devices that you can not even imagine. If they plug-in a combo USB device including an external USB hub, the whole embedded Linux system maybe crash or hang there. So this patch is to refuse enumerate such unsupported USB devices. -Bryan Wu -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/