Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755709AbXJIRkH (ORCPT ); Tue, 9 Oct 2007 13:40:07 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752314AbXJIRj4 (ORCPT ); Tue, 9 Oct 2007 13:39:56 -0400 Received: from pentafluge.infradead.org ([213.146.154.40]:43200 "EHLO pentafluge.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750930AbXJIRjz (ORCPT ); Tue, 9 Oct 2007 13:39:55 -0400 Date: Tue, 9 Oct 2007 10:39:25 -0700 From: Greg KH To: Alan Stern Cc: David Miller , David Brownell , Kernel development list , USB users list Subject: Re: [Linux-usb-users] OHCI root_port_reset() deadly loop... Message-ID: <20071009173925.GA6062@kroah.com> References: <20071008.201653.43030513.davem@davemloft.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.16 (2007-06-09) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2127 Lines: 50 On Tue, Oct 09, 2007 at 12:01:54PM -0400, Alan Stern wrote: > On Mon, 8 Oct 2007, David Miller wrote: > > > As coicidence would have it I finally found a recipe for triggering > > the issue, and it ties into what you're talking about here. > > > > It happens only if I make sure OHCI gets loaded first and then EHCI > > right afterwards. > > > > It seems that indeed it is important for EHCI to get loaded first, > > and in-kernel this is ensured by the link ordering. > > > > However, when both OHCI and EHCI are built as modules (or, similarly > > I guess, OHCI is built-in and EHCI is modular) there appears to be > > nothing in userspace which makes sure EHCI gets loaded first. > > > > When this triggers, in OHCI's root_port_reset(), the port status > > register reads 0x111 in that inner-loop and the value never changes. > > It stays like this forever. > > I agree with Ben; the best way to solve this is in the kernel. Even if > you did manage to make sure that modules were loaded in the right order > initially, that wouldn't help if somebody starts unloading and loading > modules by hand. > > The underlying cause of the problem appears to be related to the fact > that it is impossible in principle to detect a disconnect while a > full/low-speed reset is in progress. However the hardware shouldn't > rely on this, and it should fail gracefully when an unexpected > disconnect does occur. > > For example, what would the controller do if the user unplugged the USB > cable right in the middle of a reset? > > Anyway, it certainly would be easy enough to make port resets mutually > exclusive with EHCI initialization. That would work on any platform, > PCI or not. That's a good idea, any thoughts as to how to do this? I think I can find some Intel and Dell people who would be glad to test this out if you have a proposed patch. thanks, greg k-h - 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/