Messages in this thread |  | | Date | Fri, 13 Sep 2002 15:39:16 -0400 | From | Adam Kropelin <> | Subject | Streaming DMA mapping question |
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I'm working on revamping the DMA mapping of a driver and have been reading Documentation/DMA-Mapping.txt and becoming one with it. On i386 I notice the following discrepency:
According to the docs, you should either unmap or sync your DMA buffer before touching it from the host. The i386 implementation of pci_unmap is empty --no problem; there must not be any unmap work to do on this arch. But the implementation of pci_dma_sync does contain a flush_write_buffers() call. This makes me think that perhaps if I'm going to modify the buffer before I submit it back to the controller I need to do:
/* so I can read it; not necessary on i386 */ pci_dma_sync_single(...);
fiddle_with_buffer(...);
/* so adapter sees my changes; this is necessary on i386 */ pci_dma_sync_single(...);
Otherwise I don't see why it is safe to touch the buffer after pci_unmap.
Someone lend me a clue?
--Adam - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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