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@xxxxxxxxx. 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: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>