From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1423064AbXDXTaH (ORCPT ); Tue, 24 Apr 2007 15:30:07 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1423063AbXDXTaH (ORCPT ); Tue, 24 Apr 2007 15:30:07 -0400 Received: from mx2.suse.de ([195.135.220.15]:47686 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1423064AbXDXTaD (ORCPT ); Tue, 24 Apr 2007 15:30:03 -0400 From: Andi Kleen Organization: SUSE Linux Products GmbH, Nuernberg, GF: Markus Rex, HRB 16746 (AG Nuernberg) To: Ashok Raj Subject: Re: [Intel IOMMU][patch 4/8] Supporting Zero Length Reads in Intel IOMMU. Date: Tue, 24 Apr 2007 21:28:11 +0200 User-Agent: KMail/1.9.6 Cc: linux-kernel@vger.kernel.org, akpm@osdl.org, gregkh@suse.de, muli@il.ibm.com, asit.k.mallick@intel.com, suresh.b.siddha@intel.com, anil.s.keshavamurthy@intel.com, arjan@linux.intel.com, shaohua.li@intel.com References: <20070424060259.426374000@intel.com> <20070424061037.821838000@intel.com> In-Reply-To: <20070424061037.821838000@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-15" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200704242128.12057.ak@suse.de> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Tuesday 24 April 2007 08:03:03 Ashok Raj wrote: > PCI specs permit zero length reads (ZLR) even if the mapping for that region > is write only. Support for this feature is indicated by the presence of a bit > in the DMAR capability. If a particular DMAR does not support this capability > we map write-only regions as read-write. > > This option can also provides a workaround for some drivers that request > a write-only mapping when they really should request a read-write. > (We ran into one such case in eepro100.c in handling rx_ring_dma) Better just fix the drivers instead of adding such hacks -Andi