Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755529AbYCZWbY (ORCPT ); Wed, 26 Mar 2008 18:31:24 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752978AbYCZWbR (ORCPT ); Wed, 26 Mar 2008 18:31:17 -0400 Received: from gate.crashing.org ([63.228.1.57]:39250 "EHLO gate.crashing.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752443AbYCZWbQ (ORCPT ); Wed, 26 Mar 2008 18:31:16 -0400 Subject: Re: [patch] pci: revert "PCI: remove transparent bridge sizing" From: Benjamin Herrenschmidt Reply-To: benh@kernel.crashing.org To: Alan Cox Cc: Linus Torvalds , Ivan Kokshaysky , Gary Hade , Ingo Molnar , Thomas Meyer , Stefan Richter , Thomas Gleixner , "Rafael J. Wysocki" , LKML , Adrian Bunk , Andrew Morton , Natalie Protasevich , pm@debian.org In-Reply-To: <20080326220738.060d00ef@core> References: <20080325201125.GD15330@elte.hu> <20080325202954.GA22007@elte.hu> <47E969E1.6080608@m3y3r.de> <20080326101450.GA9060@jurassic.park.msu.ru> <20080326135458.GA27621@elte.hu> <20080326180701.GA6249@us.ibm.com> <20080326203012.GB6249@us.ibm.com> <20080326205828.GA15225@jurassic.park.msu.ru> <1206568675.6926.7.camel@pasglop> <20080326220738.060d00ef@core> Content-Type: text/plain Date: Thu, 27 Mar 2008 09:27:28 +1100 Message-Id: <1206570448.6926.27.camel@pasglop> Mime-Version: 1.0 X-Mailer: Evolution 2.12.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1402 Lines: 31 On Wed, 2008-03-26 at 22:07 +0000, Alan Cox wrote: > > PCI bridges at zero is perfectly valid indeed and I'm sure we have that > > around at least for IO space. In fact, I'm surprised you don't have that > > on x86. Typically, things like an HT segment with a P2P bridge and > > behind that bridge an ISA bridge could well have the P2P bridge with a > > resource forwarding 0...0x1000 IO downstream for example even on x86 > > no ? (I'm not -that- familiar with the crazyness of legacy ISA on x86 > > but I've definitely seen such setup on other archs). > > On a PC system 0x00-0xFF are motherboard resources (sometimes chipset, > some even swallowed by the CPU in certain cases) so 0 as disabled is sort > of safe but as shown by the pci_enable_device_bars replacement code - not > a good idea neccessarily. > > A lot of driver code does assume 0 == unavailable/off/disabled including > large chunks of serial, ata, ide and probably other subsystems. True, and we do try to avoid allocating resources at 0 most of the time, but it happens, and in the case of bridges, it can make somewhat sense (more in fact than for devices I'd say). Cheers, Ben. -- 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/