From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Thu, 28 Jun 2001 18:49:02 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Thu, 28 Jun 2001 18:48:53 -0400 Received: from pizda.ninka.net ([216.101.162.242]:20382 "EHLO pizda.ninka.net") by vger.kernel.org with ESMTP id ; Thu, 28 Jun 2001 18:48:41 -0400 From: "David S. Miller" MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Message-ID: <15163.46150.164836.342792@pizda.ninka.net> Date: Thu, 28 Jun 2001 15:48:38 -0700 (PDT) To: Ben LaHaise Cc: Jes Sorensen , "MEHTA,HIREN (A-SanJose,ex1)" , "'linux-kernel@vger.kernel.org'" Subject: Re: (reposting) how to get DMA'able memory within 4GB on 64-bit m achi ne In-Reply-To: In-Reply-To: <15163.45534.977835.569473@pizda.ninka.net> X-Mailer: VM 6.75 under 21.1 (patch 13) "Crater Lake" XEmacs Lucid Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Ben LaHaise writes: > > How do you represent this with the undocumented API ia64 has decided > > to use? You can't convey this information to the driver, because the > > driver may say "I don't care if it's slower, I want the large > > addressing because otherwise I'd consume or overflow the IOMMU > > resources". How do you say "SAC is preferred for performance" with > > ia64's API? You can't. > > How is SAC useful on ia64? All the machines are going to be shipped with > more than 4GB of RAM, and they need an IOMMU. That is all that some devices are able to do, especially sound cards, some of which even have < 32-bit addressing limitations. ia64 supports such devices just fine, I know it does, else you couldn't stick an eepro100 into an ia64 box running Linux :-) There is a software IOMMU implemented in the ia64 port, and it handles such SAC situations today. > Like it or not, 64 bit DMA is here, NOW. Not during the 2.6, but during > 2.4. We can either start fixing the ia64 APIs and replacing them with > something that's "Right" or we can continue with ad hoc solutions. It will be fixed in 2.5.x and backported perhaps to 2.4.x, 2.4.x is not a place for API experimentation. Later, David S. Miller davem@redhat.com