On Thu, Jan 25, 2018 at 04:44:36PM +0800, Huacai Chen wrote: > 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. I also see there is a dma_sync_*_for_{cpu,device} to avoid "mapping" and "unmapping" the same area repeatedly if it is reused. > 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? Yeh, I suppose thats effectively what it should do (though probably via an arch specific function rather than dma_cache_sync() itself). Also the sync_*_for_{cpu,device} callbacks should probably do it too. See all the calls to __dma_sync() in the MIPS dma-default.c implementation. Cheers James > > 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. > >> >
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