Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756464Ab0DEUAo (ORCPT ); Mon, 5 Apr 2010 16:00:44 -0400 Received: from imr2.ericy.com ([198.24.6.3]:46214 "EHLO imr2.ericy.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755918Ab0DEUAk (ORCPT ); Mon, 5 Apr 2010 16:00:40 -0400 Subject: Re: [PATCH][RESEND] x86: Do not write to VGA memory space if CONFIG_VGA_CONSOLE is undefined From: Guenter Roeck Reply-To: guenter.roeck@ericsson.com To: linux-kernel@vger.kernel.org, hpa@zytor.com CC: penberg@cs.helsinki.fi, mingo@redhat.com, x86@kernel.org In-Reply-To: <4BBA3021.9090504@zytor.com> References: <1270046479-4486-1-git-send-email-guenter.roeck@ericsson.com> <84144f021003310832i3420e4c1g7396b4d1f311f393@mail.gmail.com> <1270491029.1477.453.camel@groeck-laptop> <4BBA3021.9090504@zytor.com> Content-Type: text/plain Organization: Ericsson Date: Mon, 5 Apr 2010 13:02:05 -0700 Message-ID: <1270497725.1477.488.camel@groeck-laptop> MIME-Version: 1.0 X-Mailer: Evolution 2.26.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2514 Lines: 60 On Mon, 2010-04-05 at 14:46 -0400, H. Peter Anvin wrote: > On 04/05/2010 11:10 AM, Guenter Roeck wrote: > > On Wed, 2010-03-31 at 11:32 -0400, Pekka Enberg wrote: > >> On Wed, Mar 31, 2010 at 4:41 PM, Guenter Roeck > >> wrote: > >>> Current early_printk code writes into VGA memory space even > >>> if CONFIG_VGA_CONSOLE is undefined. This can cause problems > >>> if there is no VGA device in the system, especially if the memory > >>> is used by another device. > >>> > >>> Fix problem by redirecting output to early_serial_console > >>> if CONFIG_VGA_CONSOLE is undefined. > >>> > >>> Signed-off-by: Guenter Roeck > >> > >> Reviewed-by: Pekka Enberg > >> > > What will it take to get this patch into the tree ? > > > > If there are coding style issues or some other unresolved concerns, > > please let me know. > > > > You didn't answer my question (c). > > I want to know how you ended up with > boot_params.screen_info.orig_video_isVGA == 1 on a system with no VGA, > which seems like it would have resolved this. > > I am *not* inclined to add a compile-time test for what should have been > handed with a runtime test already. > Sorry, I thought I did answer it. The problem is that early_printk() can be called prior to the call to setup_early_printk(). Since early_console is currently pre-initialized with early_vga_console, output can be written to VGA memory space even if there is no VGA controller in the system (and even if boot_params.screen_info.orig_video_isVGA == 0). This happens for all early_printk() calls executed prior to the call to setup_early_printk(). I don't mind taking out have_vga_console, if that is the issue. That is just an optimization resulting in the entire VGA code to be optimized away if CONFIG_VGA_CONSOLE is not defined. The important part of the patch is to not pre-initialize early_console with early_vga_console if CONFIG_VGA_CONSOLE is not defined. An alternative might be to not pre-initialize early_console at all, and to modify early_printk() to not do anything if early_console is NULL. However, that would result in output such as "Kernel alive" to not be displayed at all, which I assumed would be undesirable. Guenter -- 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/