From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754617Ab1EYXFr (ORCPT ); Wed, 25 May 2011 19:05:47 -0400 Received: from one.firstfloor.org ([213.235.205.2]:47286 "EHLO one.firstfloor.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751885Ab1EYXFq (ORCPT ); Wed, 25 May 2011 19:05:46 -0400 Date: Thu, 26 May 2011 01:05:44 +0200 From: Andi Kleen To: Daniel Haid Cc: Konrad Rzeszutek Wilk , Andi Kleen , linux-kernel@vger.kernel.org Subject: Re: Question about iommu on x86_64 and radeon driver. Message-ID: <20110525230544.GA4065@one.firstfloor.org> References: <6ac3f6faad655602b767aa14b355e982@admin.gogi.tv> <20110523220536.GB11961@dumpdata.com> <756073831c36e0404199a4e8239bcb70@admin.gogi.tv> <08370791664f069624d25c757ed101c0@admin.gogi.tv> <20110525125752.GB3467@dumpdata.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.4.2.2i Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, May 25, 2011 at 09:21:21PM +0100, Daniel Haid wrote: > >Only if you allow 3GB or less in the machine. So you would have to do > >mem=3G as well. > > > >The reason is that (and you can see that yourself by looking at the > >E820), is that 1GB is actually _above_ the 4GB. > > Just another question on this one: > > Why can a driver not simply ask for DMA-capable memory, is this not > what memory zones are for? In many cases the memory gets passed into the driver. If it's not already in the right boundaries it would need to copy through a bounce buffer. That is what swiotlb does, if there's no IOMMU. -Andi