From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mout.kundenserver.de ([212.227.126.130]:56854 "EHLO mout.kundenserver.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750910AbaEGH70 (ORCPT ); Wed, 7 May 2014 03:59:26 -0400 From: Arnd Bergmann To: Bjorn Helgaas Cc: linux-doc@vger.kernel.org, Greg Kroah-Hartman , Joerg Roedel , Randy Dunlap , Liviu Dudau , linux-kernel@vger.kernel.org, James Bottomley , linux-pci@vger.kernel.org, David Woodhouse Subject: Re: [PATCH v2 4/5] iommu: Use dma_addr_t for IOVA arguments Date: Wed, 07 May 2014 09:58:58 +0200 Message-ID: <45161364.3Gyo1xJJLV@wuerfel> In-Reply-To: <20140506224840.17968.29010.stgit@bhelgaas-glaptop.roam.corp.google.com> References: <20140506223250.17968.27054.stgit@bhelgaas-glaptop.roam.corp.google.com> <20140506224840.17968.29010.stgit@bhelgaas-glaptop.roam.corp.google.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Sender: linux-pci-owner@vger.kernel.org List-ID: On Tuesday 06 May 2014 16:48:40 Bjorn Helgaas wrote: > Convert the "iova" arguments of iommu_map(), iommu_unmap(), etc., from > "unsigned long" to dma_addr_t. > > bb5547acfcd8 ("iommu/fsl: Make iova dma_addr_t in the iommu_iova_to_phys > API") did this for iommu_iova_to_phys(), but didn't fix the rest of the > IOMMU API. This patch looks 100% correct, but I'm not convinced it's a good idea: On 32-bit platforms (i.e. most of the ones you change), doing 64-bit arithmetic has a noticeable overhead. I am not aware of an IOMMU that actually uses 64-bit DMA addresses on its slave side, usually they are used to translate addresses from 32-bit masters into 64-bit memory addresses, so using 'unsigned long' seems better from a practical point of view as opposed to the strict type correctness. Arnd