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Date: Sat, 10 Jan 2009 10:30:06 +0100 From: Stefan Richter <stefanr@...6.in-berlin.de> To: Vineet Gupta <vineetg76@...il.com> CC: linux-kernel@...r.kernel.org Subject: Re: Query about DMA map API implementation in non-coherent archs Vineet Gupta wrote: ... > As per dma-mapping and dma-api docs, for streaming DMA mappings arch > needs to provide 2 seperate APIs > > 1. map API to convert cpu address into DMA address > 2. sync API to flush/invalidate the dcaches for non-coherent archs > (essentially when changing the ownership of buffer between cpu and > device). > > However from what I understood, the map API need not take care of > proper cache sync.However both ARM and MIPS do the cache sync > operations in map API as well (this is done standalone in sync APIs > too). Is there a specific reason for this. > > Drivers such as libata don't even call any sync API. For e.g. libata > only calls dma_map_sg ( ) while setting up the DMA. ... dma_map_*() transfers ownership of a buffer from CPUs to the device too. In case of DMA_TO_DEVICE or DMA_BIDIRECTIONAL, these calls therefore have to make sure that the device sees current buffer contents. -- Stefan Richter -=====-==--= ---= -=-=- http://arcgraph.de/sr/ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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