From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752588AbbEDLMJ (ORCPT ); Mon, 4 May 2015 07:12:09 -0400 Received: from 8bytes.org ([81.169.241.247]:39949 "EHLO theia.8bytes.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752303AbbEDLLr (ORCPT ); Mon, 4 May 2015 07:11:47 -0400 Date: Mon, 4 May 2015 13:11:46 +0200 From: Joerg Roedel To: Borislav Petkov Cc: =?iso-8859-1?Q?J=F6rg-Volker?= Peetz , linux-kernel@vger.kernel.org, Ingo Molnar , tglx@linutronix.de, mingo@redhat.com, hpa@zytor.com, x86@kernel.org, bhelgaas@google.com, Suravee.Suthikulpanit@amd.com Subject: Re: [PATCH] x86, aperture: Check for GART before accessing GART registers Message-ID: <20150504111146.GF15736@8bytes.org> References: <551D661D.3030000@amd.com> <20150402160634.GB8045@gmail.com> <551D6CF5.1010604@amd.com> <20150402165356.GE4579@pd.tnic> <551D7695.2010509@amd.com> <20150402171705.GF4579@pd.tnic> <552CF6DF.3000002@web.de> <20150414113349.GA26075@pd.tnic> <552D5AF8.3070705@web.de> <20150414183643.GF14069@pd.tnic> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150414183643.GF14069@pd.tnic> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Apr 14, 2015 at 08:36:43PM +0200, Borislav Petkov wrote: > 64MB out of how much? Does it even matter? > > You could turn off CONFIG_GART_IOMMU and not build aperture_64.c at all. > > I think then you'll fall back to swiotlb or whatever and that will most > likely slow down DMA ... the story was something like that, at least, > memory's hazy. Joerg's on CC, he'll correct me if I'm talking bull. Using SWIOTLB will also eat 64MB of RAM, so it doesn't matter if you use it instead of the GART driver. So whether your machine has GART or not, it will cost you 64MB of RAM for DMA remapping (unless you have a real IOMMU). Joerg