From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759560AbXLQNuW (ORCPT ); Mon, 17 Dec 2007 08:50:22 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753364AbXLQNuK (ORCPT ); Mon, 17 Dec 2007 08:50:10 -0500 Received: from mx3.mail.elte.hu ([157.181.1.138]:45229 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751381AbXLQNuI (ORCPT ); Mon, 17 Dec 2007 08:50:08 -0500 Date: Mon, 17 Dec 2007 14:49:30 +0100 From: Ingo Molnar To: Bernhard Kaindl Cc: Stefan Richter , Andi Kleen , Bernhard Kaindl , linux-kernel@vger.kernel.org, linux1394-devel@lists.sourceforge.net, Thomas Renninger , Benjamin Herrenschmidt , Thomas Gleixner , "H. Peter Anvin" Subject: Re: [PATCH] Early boot debugging via FireWire (ohci1394_dma=early) Message-ID: <20071217134929.GJ1870@elte.hu> References: <200702101242.48467.ak@suse.de> <45CDCDCD.5000609@s5r6.in-berlin.de> <4755D186.20204@s5r6.in-berlin.de> <4755D612.1090103@s5r6.in-berlin.de> <4755D757.7060002@s5r6.in-berlin.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.17 (2007-11-01) X-ELTE-VirusStatus: clean X-ELTE-SpamScore: -1.5 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-1.5 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.2.3 -1.5 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Bernhard Kaindl wrote: > Subject of this patch: > > This patch adds a new configuration option, which adds support for a > new early_param which gets checked in > arch/x86/kernel/setup_{32,64}.c:setup_arch() to decide wether > OHCI-1394 FireWire controllers should be initialized and enabled for > physical DMA access to allow remote debugging of early problems like > issues ACPI or other subsystems which are executed very early. > > If the config option is not enabled, no code is changed, and if the > boot paramenter is not given, no new code is executed, and independent > of that, all new code is freed after boot, so the config option can be > even enabled in standard, non-debug kernels. > > With specialized tools, it is then possible to get debugging > information from machines which have no serial ports (notebooks) such > as the printk buffer contents, or any data which can be referenced > from global pointers, if it is stored below the 4GB limit and even > memory dumps of of the physical RAM region below the 4GB limit can be > taken without any cooperation from the CPU of the host, so the machine > can be crashed early, it does not matter. cool stuff! I've tentatively added your patch to x86.git (pending more review feedback from others), but it already looks quite nice to me. Ingo