Thx Arnd, On Tue, Jul 30, 2019 at 11:22 PM Arnd Bergmann <arnd@xxxxxxxx> wrote: > > On Tue, Jul 30, 2019 at 5:11 PM Guo Ren <guoren@xxxxxxxxxx> wrote: > > > > diff --git a/arch/csky/mm/dma-mapping.c b/arch/csky/mm/dma-mapping.c > > > > cache_op(paddr, size, dma_wb_range); > > > > break; > > > > case DMA_FROM_DEVICE: > > > > + cache_op(paddr, size, dma_inv_range); > > > > + break; > > > > case DMA_BIDIRECTIONAL: > > > > cache_op(paddr, size, dma_wbinv_range); > > > > break; > > > > > > When syncing 'for_cpu', you should not need to write back, because > > > there won't be any dirty cache lines. > > > > I just follow the dma_data_direction param, seems dir param and > > function are a little bit duplicated. And our cpu won't clear clean > > cache line into memory, so dma_wb_page won't cause problem. > > Seems arch_sync_dma_for_cpu with dir=DMA_TO_DEVICE is > > self-contradictory. > > Right, you generally don't need to do cache management for that > combination. > > There might be other things to do here though, e.g. with a strict > iommu implementation one could tear down the i/o page table > entry to prevent the device from accessing a buffer while that is > owned by the cpu. Tear down i/o page table shouldn't be put here and it's for map/unmap(). And I think arch_sync_dma_for_cpu/device should only do cache issues. -- Best Regards Guo Ren ML: https://lore.kernel.org/linux-csky/
