From: Petr Tesařík <p...@tesarici.cz> Sent: Monday, April 15, 2024 4:46 AM > > Hi Michael, > > sorry for taking so long to answer. Yes, there was no agreement on the > removal of the "dir" parameter, but I'm not sure it's because of > symmetry with swiotlb_sync_*(), because the topic was not really > discussed. > > The discussion was about the KUnit test suite and whether direction is > a property of the bounce buffer or of each sync operation. Since DMA API > defines associates each DMA buffer with a direction, the direction > parameter passed to swiotlb_sync_*() should match what was passed to > swiotlb_tbl_map_single(), because that's how it is used by the generic > DMA code. In other words, if the parameter is kept, it should be kept > to match dma_map_*(). > > However, there is also symmetry with swiotlb_tbl_unmap_single(). This > function does use the parameter for the final sync. I believe there > should be a matching initial sync in swiotlb_tbl_map_single(). In > short, the buffer sync for DMA non-coherent devices should be moved from > swiotlb_map() to swiotlb_tbl_map_single(). If this sync is not needed, > then the caller can (and should) include DMA_ATTR_SKIP_CPU_SYNC in > the flags parameter. > > To sum it up: > > * Do *NOT* remove the "dir" parameter. > * Let me send a patch which moves the initial buffer sync. >
I'm not seeing the need to move the initial buffer sync. All callers of swiotlb_tbl_map_single() already have a subsequent check for a non-coherent device, and a call to arch_sync_dma_for_device(). And the Xen code has some special handling that probably shouldn't go in swiotlb_tbl_map_single(). Or am I missing something? Michael
