From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail137.messagelabs.com (mail137.messagelabs.com [216.82.249.19]) by kanga.kvack.org (Postfix) with SMTP id AE7FB90023D for ; Fri, 24 Jun 2011 11:47:23 -0400 (EDT) From: Arnd Bergmann Subject: Re: [PATCH 5/8] ARM: dma-mapping: move all dma bounce code to separate dma ops structure Date: Fri, 24 Jun 2011 17:47:02 +0200 References: <1308556213-24970-1-git-send-email-m.szyprowski@samsung.com> <20110620144247.GF26089@n2100.arm.linux.org.uk> <000901cc2f5f$237795a0$6a66c0e0$%szyprowski@samsung.com> In-Reply-To: <000901cc2f5f$237795a0$6a66c0e0$%szyprowski@samsung.com> MIME-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Message-Id: <201106241747.03113.arnd@arndb.de> Sender: owner-linux-mm@kvack.org List-ID: To: Marek Szyprowski Cc: 'Russell King - ARM Linux' , linux-arm-kernel@lists.infradead.org, linaro-mm-sig@lists.linaro.org, linux-mm@kvack.org, linux-arch@vger.kernel.org, 'Kyungmin Park' , 'Joerg Roedel' On Monday 20 June 2011, Marek Szyprowski wrote: > On Monday, June 20, 2011 4:43 PM Russell King - ARM Linux wrote: > > > On Mon, Jun 20, 2011 at 09:50:10AM +0200, Marek Szyprowski wrote: > > > This patch removes dma bounce hooks from the common dma mapping > > > implementation on ARM architecture and creates a separate set of > > > dma_map_ops for dma bounce devices. > > > > Why all this additional indirection for no gain? > > I've did it to really separate dmabounce code and let it be completely > independent of particular internal functions of the main generic dma-mapping > code. > > dmabounce is just one of possible dma-mapping implementation and it is really > convenient to have it closed into common interface (dma_map_ops) rather than > having it spread around and hardcoded behind some #ifdefs in generic ARM > dma-mapping. > > There will be also other dma-mapping implementations in the future - I > thinking mainly of some iommu capable versions. > > In terms of speed I really doubt that these changes have any impact on the > system performance, but they significantly improves the code readability > (see next patch with cleanup of dma-mapping.c). Yes. I believe the main effect of splitting out dmabounce into its own set of operations is improved readability for people that are not familiar with the existing code (which excludes Russell ;-) ), by separating the two codepaths and losing various #ifdef. The simplification becomes more obvious when you look at patch 6, which removes a lot of the code that becomes redundant after this one. Still, patches 5 and 6 are certainly not essential, nothing depends on that and if Russell still doesn't like them, they can easily be dropped. 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