From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Mon, 21 May 2001 09:57:35 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Mon, 21 May 2001 09:57:25 -0400 Received: from geos.coastside.net ([207.213.212.4]:48117 "EHLO geos.coastside.net") by vger.kernel.org with ESMTP id ; Mon, 21 May 2001 09:57:17 -0400 Mime-Version: 1.0 Message-Id: In-Reply-To: <15112.60362.447922.780857@pizda.ninka.net> In-Reply-To: <20010520044013.A18119@athlon.random> <3B07AF49.5A85205F@uow.edu.au> <20010520154958.E18119@athlon.random> <3B07CF20.2ABB5468@uow.edu.au> <20010520163323.G18119@athlon.random> <15112.26868.5999.368209@pizda.ninka.net> <20010521034726.G30738@athlon.random> <15112.48708.639090.348990@pizda.ninka.net> <20010521105944.H30738@athlon.random> <15112.55709.565823.676709@pizda.ninka.net> <20010521115631.I30738@athlon.random> <15112.59880.127047.315855@pizda.ninka.net> <15112.60362.447922.780857@pizda.ninka.net> Date: Mon, 21 May 2001 06:55:29 -0700 To: "David S. Miller" , Andrea Arcangeli , Andrew Morton , Ivan Kokshaysky , Richard Henderson , linux-kernel@vger.kernel.org From: Jonathan Lundell Subject: Re: alpha iommu fixes Content-Type: text/plain; charset="us-ascii" ; format="flowed" Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org At 3:19 AM -0700 2001-05-21, David S. Miller wrote: >This is totally wrong in two ways. > >Let me fix this, the IOMMU on these machines is per PCI bus, so this >figure should be drastically lower. > >Electrically (someone correct me, I'm probably wrong) PCI is limited >to 6 physical plug-in slots I believe, let's say it's 8 to choose an >arbitrary larger number to be safe. > >Then we have: > >max bytes per bttv: max_gbuffers * max_gbufsize > 64 * 0x208000 == 133.12MB > >133.12MB * 8 PCI slots == ~1.06 GB > >Which is still only half of the total IOMMU space available per >controller. 8 slots (and you're right, 6 is a practical upper limit, fewer for 66 MHz) *per bus*. Buses can proliferate like crazy, so the slot limit becomes largely irrelevant. A typical quad Ethernet card, for example (and this is true for many/most multiple-device cards), has a bridge, its own internal PCI bus, and four "slots" ("devices" in PCI terminology). -- /Jonathan Lundell.