Hi Huacai, On Thu, Jan 25, 2018 at 03:09:33PM +0800, Huacai Chen wrote: > Hi, James and Christoph, > > We have modified arch/mips/loongson64/common/dma-swiotlb.c to make > Loongson support coherent&non-coherent devices co-exist. You can see > code here: > https://github.com/linux-loongson/linux-loongson/commit/3f212e36b2432a7c4a843649e4b79c9c0837d1d2 > When device is non-coherent, we will call dma_cache_sync(). > > Then, if dma_cache_sync() is only designed for > DMA_ATTR_NON_CONSISTENT, what can I use? How did you allocate the memory? The appropriate generic API for the type of memory should always be used in drivers over arch specific stuff. AFAIK (see e.g. Documentation/DMA-API.txt): - dma_alloc_coherent() shouldn't require syncing, though it may require flushing of write combiners - dma_alloc_attrs() only requires syncing when DMA_ATTR_NON_CONSISTENT is used, otherwise is the same as dma_alloc_coherent() - guaranteed contiguous memory within PA range (e.g. kmalloc()'d memory with the appropriate GFP_DMA flags) can be synced using the dma_map_*() and dma_unmap_*() functions. Cheers James > 1, __dma_sync_virtual() and __dma_sync() are both static functions, so > can't be called in other files. > 2, mips_dma_cache_sync() is not static, but I think it isn't designed > to be called directly (So it should be static). > 3, dma_cache_wback(), dma_cache_inv() and dma_cache_wback_inv() does't > take a "direction" argument, so I should determine the direction first > (then I will reimplement __dma_cache_sync for myself). > So, It seems that I can only use dma_cache_sync(). > > Huacai > > On Wed, Jan 24, 2018 at 11:29 PM, Christoph Hellwig <hch@xxxxxx> wrote: > > On Wed, Jan 24, 2018 at 03:03:05PM +0000, James Hogan wrote: > >> I see, that makes sense. Thanks Christoph. I'll assume this patch isn't > >> applicable then unless Huacai adds some explanation. > > > > In addition there also is no driver that can be used on loongsoon > > that actually calls dma_cache_sync either. > >
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