From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx187.postini.com [74.125.245.187]) by kanga.kvack.org (Postfix) with SMTP id D31846B004A for ; Wed, 11 Apr 2012 08:19:04 -0400 (EDT) From: Arnd Bergmann Subject: Re: [PATCHv8 04/10] ARM: dma-mapping: remove offset parameter to prepare for generic dma_ops Date: Wed, 11 Apr 2012 12:18:39 +0000 References: <1334055852-19500-1-git-send-email-m.szyprowski@samsung.com> <201204101143.27915.arnd@arndb.de> <012e01cd17db$5f165c30$1d431490$%szyprowski@samsung.com> In-Reply-To: <012e01cd17db$5f165c30$1d431490$%szyprowski@samsung.com> MIME-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Message-Id: <201204111218.39800.arnd@arndb.de> Sender: owner-linux-mm@kvack.org List-ID: To: Marek Szyprowski Cc: linux-arm-kernel@lists.infradead.org, linaro-mm-sig@lists.linaro.org, linux-mm@kvack.org, linux-arch@vger.kernel.org, iommu@lists.linux-foundation.org, 'Kyungmin Park' , 'Joerg Roedel' , 'Russell King - ARM Linux' , 'Chunsang Jeong' , 'Krishna Reddy' , 'KyongHo Cho' , Andrzej Pietrasiewicz , 'Benjamin Herrenschmidt' , 'Konrad Rzeszutek Wilk' , 'Hiroshi Doyu' , 'Subash Patel' On Wednesday 11 April 2012, Marek Szyprowski wrote: > Well, range sync functions are available from the early days of the dma > mapping api (at least that's what I've found reading the change log and > old patches). They are the correct way of doing a partial syncs on the > buffer (usually used by the network device drivers). This patch changes > only the internal implementation of the dma bounce functions to let > them tunnel through dma_map_ops structure. The driver api stays > unchanged, so driver are obliged to call dma_*_range_* functions to > keep code clean and easy to understand. > > The only drawback I can see from this patch is reduced detection of > the dma api abuse. Let us consider the following code: > > dma_addr = dma_map_single(dev, ptr, 64, DMA_TO_DEVICE); > dma_sync_single_range_for_cpu(dev, dma_addr+16, 0, 32, DMA_TO_DEVICE); > > Without the patch such code fails, because dma bounce code is unable > to find the bounce buffer for the given dma_address. After the patch > the sync call will be equivalent to: > > dma_sync_single_range_for_cpu(dev, dma_addr, 16, 32, DMA_TO_DEVICE); > > which succeeds. > > I don't consider this as a real problem. DMA API abuse should be caught > by debug_dma_* function family, so we can simplify the internal low-level > implementation without losing anything. > Ok, fair enough. Can you put the above text into the changelog? Arnd -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org