Hi there, I was wondering whether setting DMA attributes like DMA_ATTR_WRITE_BARRIER will have an effect if I don't dma_unmap_single_attr() an area but merely dma_sync_single() it after a transfer from the device to the host memory. My problem is that I get an interrupt (MSI) indicating that an (independent) DMA transfer is done, where the interrupt flags get pushed (via a DMA write) to host memory.
From time to time, the data of the other DMA transfer does not show up in host memory in time with the interrupt. I am trying to force coherency by using the DMA_ATTR_WRITE_BARRIER on this status push (of the interrupt flags), to force the other writes (device to host) to complete.
Does that seem reasonable? Can anyone with insight shine some light on that? It's a PCIe device, I'm running Fedora 18 with 3.8.3-201.fc18.x86_64. Cheers, Moritz