> -----Original Message----- > From: Laura Abbott [mailto:lauraa@xxxxxxxxxxxxxx] > Sent: Friday, July 20, 2012 10:30 PM > To: Marek Szyprowski > Cc: linaro-mm-sig@xxxxxxxxxxxxxxxx; 'Russell King'; linux-arm-msm@xxxxxxxxxxxxxxx; linux-arm- > kernel@xxxxxxxxxxxxxxxxxxx > Subject: Re: [PATCH][RFC] arm: dma-mapping: Add support for allocating/mapping cached buffers > > On 7/16/2012 10:58 PM, Marek Szyprowski wrote: > > Hi Laura, > > > > On Friday, July 13, 2012 8:02 PM Laura Abbott wrote: > > > >> There are currently no dma allocation APIs that support cached > >> buffers. For some use cases, caching provides a signficiant > >> performance boost that beats write-combining regions. Add > >> apis to allocate and map a cached DMA region. > >> > >> Signed-off-by: Laura Abbott <lauraa@xxxxxxxxxxxxxx> > > > > I agree that there is a need for cached contiguous memory blocks. I see that your patch > > is based on some older version of CMA/dma-mapping code. In v3.5-rc1 CMA has been merged > > to mainline kernel together with DMA-mapping redesign patches, so an attribute approach > > can be used instead of adding new functions to the API. My original idea was to utilize > > the dma_alloc_nonconsistent() call and DMA_ATTR_NONCONSISTENT for allocating/mapping > > cached contiguous buffers, but I didn't have enough time for completing this work. > > > > The main missing piece is the API for managing cache synchronization on such buffers. > > There is a dma_cache_synch() functions but it is broken from the API point of view. To > > replace it with something better, some additional work is needed for all drivers which > > already use it. Also some work in needed for cleanup dma_alloc_nonconsistent() > > implementations for all the architectures using dma_map_ops approach. All this is on my > > TODO list, but I currently I'm really busy with other tasks related to CMA (mainly > > bugfixes for some special use-cases). > > > > In what is the dma_cache_sync API broken? Just curious at this point. There are two issues with it: 1. There is no clear buffer ownership definition like it is done for dma_sync_single_for_cpu/device() functions. 2. DMA address argument is missing, which is required for clean and robust implementation on some architectures. I would like to completely remove dma_cache_sync() and replace it with dma_sync_single_for_cpu/device(), but this probably require a bit more discussion and fixing all current clients of dma_cache_sync(). Best regards -- Marek Szyprowski Samsung Poland R&D Center -- To unsubscribe from this list: send the line "unsubscribe linux-arm-msm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html