From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755947Ab1KBRVu (ORCPT ); Wed, 2 Nov 2011 13:21:50 -0400 Received: from caramon.arm.linux.org.uk ([78.32.30.218]:39624 "EHLO caramon.arm.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755630Ab1KBRVu (ORCPT ); Wed, 2 Nov 2011 13:21:50 -0400 Date: Wed, 2 Nov 2011 17:21:42 +0000 From: Russell King - ARM Linux To: Catalin Marinas Cc: linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH v7 16/16] ARM: LPAE: Add the Kconfig entries Message-ID: <20111102172142.GB12913@n2100.arm.linux.org.uk> References: <1312988619-16804-1-git-send-email-catalin.marinas@arm.com> <1312988619-16804-17-git-send-email-catalin.marinas@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1312988619-16804-17-git-send-email-catalin.marinas@arm.com> User-Agent: Mutt/1.5.19 (2009-01-05) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Aug 10, 2011 at 04:03:39PM +0100, Catalin Marinas wrote: > +config ARCH_DMA_ADDR_T_64BIT > + def_bool ARM_LPAE > + I think this should be selected only when we have a DMA engine supporting 64-bit addresses. Technically LPAE itself doesn't give us that assurance. If you have this kind of a setup: CPU <==++==> RAM || IOMMU | DMA device where == and || means >32-bit addressing, and | means 32-bit addressing. In such a setup, having dma_addr_t be 64-bit is pointless because it should never see 64-bit addresses (the DMA API should deal with the IOMMU and provide a list of DMA addresses to be placed into RAM for the DMA device which takes account of the mappings setup in the IOMMU.) So, I think 64-bit dma_addr_t should be a property of the DMA devices present in the system rather than whether the CPUs MMU can deal with >32-bit addresses or not.