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[209.132.180.67]) by mx.google.com with ESMTP id 85si17825725pgd.84.2019.04.16.08.02.05; Tue, 16 Apr 2019 08:02:23 -0700 (PDT) Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67; Authentication-Results: mx.google.com; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729939AbfDPPAm (ORCPT + 99 others); Tue, 16 Apr 2019 11:00:42 -0400 Received: from iolanthe.rowland.org ([192.131.102.54]:42770 "HELO iolanthe.rowland.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1729742AbfDPPAg (ORCPT ); Tue, 16 Apr 2019 11:00:36 -0400 Received: (qmail 5287 invoked by uid 2102); 16 Apr 2019 11:00:35 -0400 Received: from localhost (sendmail-bs@127.0.0.1) by localhost with SMTP; 16 Apr 2019 11:00:35 -0400 Date: Tue, 16 Apr 2019 11:00:35 -0400 (EDT) From: Alan Stern X-X-Sender: stern@iolanthe.rowland.org To: Jesse Hathaway cc: Bjorn Helgaas , Ingo Molnar , Peter Zijlstra , , , Mathias Nyman , Greg Kroah-Hartman , Subject: Re: Regression causes a hang on boot with a Comtrol PCI card In-Reply-To: Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 15 Apr 2019, Jesse Hathaway wrote: > On Sat, Apr 6, 2019 at 10:32 AM Alan Stern wrote: > > Well, at least that's forward progress. I don't know what pstore is or > > what connection it has to the USB subsystem. Does the machine hang > > similarly if you boot without the Comtrol PCI card present? > > Yes the box boots fine when the Comtrol PCI card is *not* present. > > > For that matter, what happens if you remove EHCI from the kernel > > configuration completely? > > If I remove USB support, the box still hangs after registering the pstore, but > if I remove pstore support and APEI support from the kernel then the box boots > without issue. > > > As for how the PCI card affects the USB handoff, it depends on how the > > BIOS behaves. Normally the BIOS will take control of all the available > > EHCI controllers during bootup (so that it can use them to communicate > > with a USB keyboard or mouse), including controllers on add-on PCI > > cards as well as those on the motherboard. When the kernel starts up, > > it tries to take ownership of the controllers away from the BIOS > > (that's the handoff) so that Linux can use them. However, if the BIOS > > was never tested for handoff of USB controllers on add-on PCI cards, it > > could easily have a bug that would crash the machine. > > The Comtrol card provides 32 serial ports, via a breakout box, but it has > no USB functionality, which was why I was surprised that its presence > somehow breaks the USB hand off. Well, I am completely mystified. Nor do I understand how the commits you identified could be related, although maybe the relationship is very indirect. Whatever the source of the problem, I don't think you're going to find it by looking at the USB code. Perhaps the early initialization of the functions that _are_ present on the Comtrol card somehow messes up other parts of the system. Alan Stern