From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933643AbZHEHJD (ORCPT ); Wed, 5 Aug 2009 03:09:03 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S933619AbZHEHJD (ORCPT ); Wed, 5 Aug 2009 03:09:03 -0400 Received: from bombadil.infradead.org ([18.85.46.34]:40752 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933515AbZHEHJB (ORCPT ); Wed, 5 Aug 2009 03:09:01 -0400 Subject: Re: [Xen-devel] Re: [RFC] Make AGP work with IOMMU From: David Woodhouse To: Dave Airlie Cc: Jeremy Fitzhardinge , Keir Fraser , xen-devel@lists.xensource.com, Joerg Roedel , iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org, Zhenyu Wang In-Reply-To: <21d7e9970908042357m6080e88fyeaaad171888766f2@mail.gmail.com> References: <1248707041.6100.35.camel@macbook.infradead.org> <21d7e9970907282328l4a44b9a2of4500c5c84a3586b@mail.gmail.com> <1248851712.19733.214.camel@macbook.infradead.org> <21d7e9970907290143q6778511cvda1c6b915f61654a@mail.gmail.com> <1248860205.19733.238.camel@macbook.infradead.org> <4A78C9C6.6010103@goop.org> <1249454696.9324.325.camel@macbook.infradead.org> <21d7e9970908042357m6080e88fyeaaad171888766f2@mail.gmail.com> Content-Type: text/plain Date: Wed, 05 Aug 2009 08:08:51 +0100 Message-Id: <1249456131.9324.332.camel@macbook.infradead.org> Mime-Version: 1.0 X-Mailer: Evolution 2.26.3 (2.26.3-1.fc11) Content-Transfer-Encoding: 7bit X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2009-08-05 at 16:57 +1000, Dave Airlie wrote: > On Wed, Aug 5, 2009 at 4:44 PM, David Woodhouse wrote: > > On Tue, 2009-08-04 at 16:52 -0700, Jeremy Fitzhardinge wrote: > >> And just when I have patches to use them for their original purpose... > >> > >> Looking back over the thread, are you saying that most users are already > >> using the DMA API correctly for AGP accesses? If that's true then we > >> should be just fine. > > > > No, not 'most users'. But perhaps we should. > > > > All we've done so far is make intel-agp use the DMA API correctly. And > > that's conditional on CONFIG_DMAR. But we could make it unconditional, > > and make the other drivers do it too. The code is all fairly generic. > > > > Without an IOMMU, the overhead would be fairly minimal. > > > > I'm not sure how prevalent Xen is on AGP systems, I'm going to guess > not enough that anyone cares. Intel integrated chips are the only AGP > codebase user that are made any more, and they don't really use AGP > its just a legacy of the previous designs. On the other hand, extending the existing code so that it uses the DMA API correctly _unconditionally_ rather than only for the Intel driver would be fairly simple and should be harmless... -- dwmw2