From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S935043AbXLNWkg (ORCPT ); Fri, 14 Dec 2007 17:40:36 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S934580AbXLNWgd (ORCPT ); Fri, 14 Dec 2007 17:36:33 -0500 Received: from terminus.zytor.com ([198.137.202.10]:58086 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934270AbXLNWgb (ORCPT ); Fri, 14 Dec 2007 17:36:31 -0500 Message-ID: <47630462.6040203@zytor.com> Date: Fri, 14 Dec 2007 14:32:02 -0800 From: "H. Peter Anvin" User-Agent: Thunderbird 2.0.0.9 (X11/20071115) MIME-Version: 1.0 To: Dave Airlie CC: "Siddha, Suresh B" , Dave Airlie , venkatesh.pallipadi@intel.com, ak@muc.de, ebiederm@xmission.com, rdreier@cisco.com, torvalds@linux-foundation.org, gregkh@suse.de, davej@redhat.com, mingo@elte.hu, tglx@linutronix.de, akpm@linux-foundation.org, arjan@infradead.org, jesse.barnes@intel.com, linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH 00/12] PAT 64b: PAT support for X86_64 References: <20071213235543.568682000@intel.com> <20071214220015.GD717@linux-os.sc.intel.com> <21d7e9970712141427h25c84e9g76237a93e634fa76@mail.gmail.com> In-Reply-To: <21d7e9970712141427h25c84e9g76237a93e634fa76@mail.gmail.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Dave Airlie wrote: > On Dec 15, 2007 8:00 AM, Siddha, Suresh B wrote: >> On Fri, Dec 14, 2007 at 12:28:25AM +0000, Dave Airlie wrote: >>> Yes, the main use for GPUs is to have RAM pages mapped WC, and placed into >>> a GART on the GPU side, currently for Intel IGD we are okay as the CPU can >>> access the GPU GART aperture, but other chips exist where this isn't >>> possible, I think poulsbo and possible some of the AMD IGPs.. >> Ok. So how is it working today on these platforms with no PAT support. >> Open source drivers use UC or WB on these platforms? As this RAM is not >> contiguous, one can't use MTRRs to set WC. Right? >> >> Well, if WC is needed for RAM, then we have to address it too. >> > > It doesn't work really, which is mostly the problem :) > > We mostly use UC on these pages, or WB within cache coherent domains. > mtrrs are totally useless in this situation. > In what sense does it not work? -hpa