On Thu, Jul 20, 2023 at 02:30:04AM -0400, Michael S. Tsirkin wrote: > sure, they are not hard to generate ;) > > https://lore.kernel.org/all/20230710034237.12391-11-xuanzhuo%40linux.alibaba.com Thanks, I'll chime in there. > > > Looks like there's really little else can be done: there's a > > > shared page we allow DMA into, so we sync periodically. > > > Then when we unmap we really do not need that data > > > synced again. > > > > > > What exactly is wrong with this? > > > > A "shared" page without ownership can't work with the streaming > > DMA API (dma_map_*) at all. You need to use dma_alloc_coherent > > so that it is mapped uncached. > > Hmm confused. Based on both documentation and code I think this works: > > dma_map > dma_sync > dma_sync > dma_sync > dma_sync > dma_unmap(DMA_ATTR_SKIP_CPU_SYNC) > > right? Depends on your definition of "shared". If there is always a clear owner at a given time you can games with lots of syncs that transfer ownership. If there is no clear ownership, and the "device" just DMAs into the buffer at random times and the host checks bits in there we need to map the buffer uncached. I'll chime in in the thread. > > -- > MST ---end quoted text---
