On Thu, Jan 25, 2018 at 3:55 PM, James Hogan <jhogan@xxxxxxxxxx> wrote: > 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. Yes, kmalloc()'d memory with the appropriate GFP_DMA flags can be synced using the dma_map_*() and dma_unmap_*() functions. So, loongson_dma_map_page()/loongson_dma_unmap_page() (which is the backend of dma_map_*() and dma_unmap_*()) should call dma_cache_sync() for non-coherent devices, right? Huacai > > 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. >> >
