From owner-freebsd-current@FreeBSD.ORG Wed Nov 24 15:25:01 2004 Return-Path: Delivered-To: freebsd-current@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id 47B3116A4CE for ; Wed, 24 Nov 2004 15:25:01 +0000 (GMT) Received: from harmony.village.org (rover.village.org [168.103.84.182]) by mx1.FreeBSD.org (Postfix) with ESMTP id A9BD543D45 for ; Wed, 24 Nov 2004 15:25:00 +0000 (GMT) (envelope-from imp@bsdimp.com) Received: from localhost (harmony.village.org [10.0.0.6]) by harmony.village.org (8.13.1/8.13.1) with ESMTP id iAOFLdg4055866; Wed, 24 Nov 2004 08:21:39 -0700 (MST) (envelope-from imp@bsdimp.com) Date: Wed, 24 Nov 2004 08:22:20 -0700 (MST) Message-Id: <20041124.082220.29053157.imp@bsdimp.com> To: cswiger@mac.com From: "M. Warner Losh" In-Reply-To: <41A49A7B.6020009@mac.com> References: <41A416E7.4030107@mac.com> <20041123.235250.118899687.imp@bsdimp.com> <41A49A7B.6020009@mac.com> X-Mailer: Mew version 3.3 on Emacs 21.3 / Mule 5.0 (SAKAKI) Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit cc: freebsd-current@freebsd.org Subject: Re: Transparent bridges (a. k. a. HUB-to-PCI bridges)? X-BeenThere: freebsd-current@freebsd.org X-Mailman-Version: 2.1.1 Precedence: list List-Id: Discussions about the use of FreeBSD-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 24 Nov 2004 15:25:01 -0000 In message: <41A49A7B.6020009@mac.com> Chuck Swiger writes: : M. Warner Losh wrote: : > In message: <41A416E7.4030107@mac.com> : > Chuck Swiger writes: : [ ... ] : > : A host-PCI bridge is typically part of the "southbridge" chip of modern : > : motherboards; on Intel motherboards this is also called the ICH chip, such as : > : the 82801AA/BA/CA/etc. VIA Southbridges include the VT8233/8235/8237/etc. : > : : > : A PCI-PCI bridge is commonly found on multifunction PCI cards, an example : > : would be the DEC 21151 chip found on various four-port NICs. : > : > Newer laptops (and other machines) typically have a PCI PCI bridge : > that all the builtin hardware lives behind. Many, but not all, of : > these bridges are transparent pci pci bridges, maning they act much : > like a subtractively decoded bridge. : : You are absolutely right; the impression I got was that laptops like to have : PCI-PCI bridges in order to make it easier to route interrupts for devices on : a docking station or the like. If they don't use such a PCI-PCI bridge chip, : then the laptop's BIOS needs to set up a $PIR table which routes interrupts : properly for _all_ of the possible docking station configurations and devices : to which the laptop might be attached to. : : Making things work right with a known configuration seems to be hard enough : for some vendors, so it's not surprising that pre-planning for possible future : configurations is difficult to do without using a PCI-PCI bridge to aggregate : the devices lurking behind it. Having a pci-pci bridge is no guarantee that the interrupts will be routed correctly. Many laptops route them directly, even in the face of a pci-pci bridge. The $PIR will often lists devices behind the bridge. Warner