Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1761641AbXLRRef (ORCPT ); Tue, 18 Dec 2007 12:34:35 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1760299AbXLRReU (ORCPT ); Tue, 18 Dec 2007 12:34:20 -0500 Received: from mx1.redhat.com ([66.187.233.31]:52246 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759758AbXLRReT (ORCPT ); Tue, 18 Dec 2007 12:34:19 -0500 Message-ID: <47680489.6040809@redhat.com> Date: Tue, 18 Dec 2007 12:34:01 -0500 From: Chuck Ebbert Organization: Red Hat User-Agent: Thunderbird 1.5.0.12 (X11/20071019) MIME-Version: 1.0 To: Linus Torvalds CC: linux-kernel , Ivan Kokshaysky , Daniel Ritz , Greg KH Subject: Re: PCI resource problems caused by improper address rounding References: <47671377.6000405@redhat.com> In-Reply-To: Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2257 Lines: 56 On 12/17/2007 07:57 PM, Linus Torvalds wrote: > > On Mon, 17 Dec 2007, Chuck Ebbert wrote: >> Looks like a commit that I can't find in git due to the arch merge >> has broken PCI address assignment. This patch by Richard Henderson >> against 2.6.23 fixes it for x86_64: >> >> --- linux-2.6.23.x86_64/arch/x86_64/kernel/e820.c 2007-10-09 13:31:38.000000000 -0700 >> +++ linux-2.6.23.x86_64-rth/arch/x86_64/kernel/e820.c 2007-12-15 12:37:44.000000000 -0800 >> @@ -718,8 +718,8 @@ __init void e820_setup_gap(void) >> while ((gapsize >> 4) > round) >> round += round; >> /* Fun with two's complement */ >> - pci_mem_start = (gapstart + round) & -round; >> + pci_mem_start = (gapstart + round - 1) & -round; > > No, it's very much meant to be that way. > > We do *not* want to have the PCI memory abutthe end of memory exactly. So > it leaves a gap in between "gapstart" and the actual start of PCI memory > addressing very much on purpose. > > In fact, the very commit (it's f0eca9626c6becb6fc56106b2e4287c6c784af3d in > the kernel tree) you mention actually explicitly *explains* that, although > maybe it's a bit indirect: if you start allocating PCI resources directly > after the end-of-RAM thing, you can easily end up using addresses that are > actually inside the magic stolen system RAM that is being used for UMA > video etc. > > So you very much want to have a buffer in between the end-of-RAM and the > actual start of the region we try to allocate in. > > So why do you want them to be close, anyway? > Because otherwise some video adapters with 256MB of memory end up with their resources allocated above 4GB, and that doesn't work very well. https://bugzilla.redhat.com/show_bug.cgi?id=425794#c0 > > PS. On a different topic: if you do > > git log --follow arch/x86/kernel/e820_64.c > > you'd see the history past the renames in git. Or just do a "git blame -C" > which will also follow renames (and copies). The history in the web interface just ends at the rename. -- 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/