Messages in this thread | | | From | akepner@sgi ... | Date | Tue, 18 Dec 2007 12:07:59 -0800 | Subject | Re: [RFC] dma: passing "attributes" to dma_map_* routines |
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On Tue, Dec 18, 2007 at 05:50:42PM +0100, Stefan Richter wrote:
> Do I understand correctly?: A device and the CPUs communicate via two > separate memory areas: A data buffer and a status FIFO. The NUMA > interconnect may reorder accesses of the device to the areas. (Write > accesses? Read accesses? Both?)
Yes, I think you understand. Reorderings are possible on reads and writes. Things get synced up by either an interrupt or a write to a memory region with a "barrier attribute". Memory allocated with dma_alloc_coherent() gets the barrier attribute. The idea here is to allow memory allocated with plain old malloc() or whatever to get the same attribute.
> > To ensure synchronization between device and CPUs, you want to mark a > memory area which is to be dma-mapped with a flag which says: "Writes > to the memory region will cause in-flight DMA to be flushed". Whose > writes? A write access from the device or a write access from a CPU?
A write from the device, e.g., when the device writes to indicate "data DMA is complete".
-- Arthur
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