From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1423018AbXDTATm (ORCPT ); Thu, 19 Apr 2007 20:19:42 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1423020AbXDTATl (ORCPT ); Thu, 19 Apr 2007 20:19:41 -0400 Received: from smtp1.linux-foundation.org ([65.172.181.25]:53463 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1423019AbXDTATk (ORCPT ); Thu, 19 Apr 2007 20:19:40 -0400 Date: Thu, 19 Apr 2007 17:19:20 -0700 (PDT) From: Linus Torvalds To: Greg KH cc: Jesse Barnes , Ivan Kokshaysky , Adam Jackson , linux-kernel@vger.kernel.org Subject: Re: PCI bridge range sizing bug In-Reply-To: <20070419234014.GB3215@suse.de> Message-ID: References: <1175812632.17147.12.camel@localhost.localdomain> <200704191611.52125.jesse.barnes@intel.com> <20070419234014.GB3215@suse.de> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 19 Apr 2007, Greg KH wrote: > On Thu, Apr 19, 2007 at 04:11:50PM -0700, Jesse Barnes wrote: > > On Thursday, April 5, 2007 3:37 pm Adam Jackson wrote: > > > So I'm attempting to do something fairly heinous (X server across > > > five video cards), and I hit a fun bug in bridge range setup. See > > > attached lspci and dmesg, but the short of it is I've got two VGA > > > chips on one card behind a bridge, which is itself behind a second > > > PCI bridge, and the bridge ranges get set up so that I can't map the > > > ROMs, which means I can't post them, and therefore can't use them > > > period. Ok, let me start out by saying that at this point in the development cycle (ie trying to get 2.6.21 out some day), I can't really find it in myself to care all that deeply about people doing something quote _that_ fairly heinous ;) > > > The alignment restriction on the ROMs seems a bit extreme: > > > > > > % sudo setpci -s 7:2 ROM_ADDRESS=ffffffff > > > % sudo setpci -s 7:2 ROM_ADDRESS > > > f0000001 Yeah, they seem to want 256MB. > > Yep, looks like those two devices had a problem. Supposedly they want > > to sit at 256M? Given that we're only giving each bridge 1M of memory > > space that would definitely be a problem. We should be sizing the bridge regions by how much space the devices behind the bridges actually need, BUT I can guess at two problems: - On PC's, we generally trust any BIOS setup. If the bridge has been initialized to some value that seems half-way valid we generally leave it there. Moving things around tends to cause a lot more problems than it fixes. - we normally do *not* try to assign ROM resources at all, because a number of video cards in particular do some really strange stuff with the ROMS, like share the decoders for the ROM's and the other PCI resources! IOW, I think that what happens is that the BIOS has set it up to have a 32MB window, and since the kernel doesn't think there is anything wrong with that, it leaves it well enough alone. You could try adding "pci=rom" to the kernel command line, which should make the kernel try to assign space for the roms too. I think we used to *never* assign PCI bus resources on x86, but that thing got fixed some time ago. Now I think we only re-assign them if they were unassigned *or* if the assignment wasn't working before. But I'm not 100% sure about that second part... It's been working so well that I don't think we've had a lot of problems with resource assignment lately, and I've paged it all out of my brain. Ivan, can you remind my tired old brain? Linus