Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750752AbWEDVGA (ORCPT ); Thu, 4 May 2006 17:06:00 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751175AbWEDVGA (ORCPT ); Thu, 4 May 2006 17:06:00 -0400 Received: from mx1.redhat.com ([66.187.233.31]:1195 "EHLO mx1.redhat.com") by vger.kernel.org with ESMTP id S1750752AbWEDVF7 (ORCPT ); Thu, 4 May 2006 17:05:59 -0400 Subject: Re: Add a "enable" sysfs attribute to the pci devices to allow userspace (Xorg) to enable devices without doing foul direct access From: Peter Jones To: Jon Smirl Cc: Matthew Garrett , Bjorn Helgaas , linux-pci@atrey.karlin.mff.cuni.cz, Dave Airlie , Andrew Morton , greg@kroah.com, linux-kernel@vger.kernel.org, Arjan van de Ven In-Reply-To: <9e4733910605041340r65d47209h2da079d9cf8fceae@mail.gmail.com> References: <1146300385.3125.3.camel@laptopd505.fenrus.org> <200605041309.53910.bjorn.helgaas@hp.com> <445A51F1.9040500@linux.intel.com> <200605041326.36518.bjorn.helgaas@hp.com> <9e4733910605041340r65d47209h2da079d9cf8fceae@mail.gmail.com> Content-Type: text/plain Organization: Red Hat, Inc. Date: Thu, 04 May 2006 17:05:36 -0400 Message-Id: <1146776736.27727.11.camel@localhost.localdomain> Mime-Version: 1.0 X-Mailer: Evolution 2.6.1 (2.6.1-2) Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1788 Lines: 45 On Thu, 2006-05-04 at 16:40 -0400, Jon Smirl wrote: > On 5/4/06, Matthew Garrett wrote: > > Bjorn Helgaas wrote: > > > > > There's already a "rom" file in sysfs. Could vbetool and friends > > > use that? > > > > Not if you have multiple graphics cards. > > Not true, the rom attribute maps the ROM into PCI space where ever the > kernel tells it to and reads it from there. It is the PCI VGA > emulation feature that forces the ROM to appear at C000:0. You can > have the ROM mapped and VGA emulation turned off. It doesn't matter -- you can accomplish the same thing with e.g. libx86emu and simply mapping the option rom to 0xc0000. But you want to do that in userland, not in the kernel. > This brings up another major point. X changes the PCI VGA emulation > routing from user space, another thing that it should not be doing. I > have posted patches before providing a sysfs VGA attribute on class > VGA devices. By setting the attribute to 1 you can control the active > VGA emulation device. > > This is yet another way that user space can mess up the kernel. If VGA > routing is changes under fbdev (my attribute notifies fbdev, the fbdev > code for processing the notification did get checked in) then the > console will screw up. And this change allows userland to avoid doing that. > The usual screw up is that the console goes > blank because hardware fonts are not setup correctly on the new > console. And that's completely unrelated to this problem. -- Peter - 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/