Messages in this thread | | | Subject | Re: PCI DMA to small buffers on cache-incoherent arch | From | Roland Dreier <> | Date | 10 Jun 2002 09:03:22 -0700 |
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>>>>> "Roland" == Roland Dreier <roland@topspin.com> writes:
David> For non-cacheline aligned chunks in the range "start" to David> "end" you must perform a cache writeback and invalidate. To David> preserve the data outside of the DMA range.
Roland> Doesn't this still have a problem if you touch data in the Roland> same cache line as the DMA buffer after the pci_map but Roland> before the DMA takes place? The CPU will pull the cache Roland> line back in and it might not see the data the DMA brought Roland> in.
Roland> It seems to me that to be totally safe, pci_unmap would Roland> have to save the non-aligned part outside the buffer to Roland> temporary storage, do an invalidate, and then copy back Roland> the non-aligned part.
Replying to myself.... Anyway, I realized that even my idea above is wrong. I don't see _any_ safe way to share a cache line between a DMA buffer and other data. Access to the cache line might pull the cache line back in and write it back at any time, which could corrupt the DMA'ed data. I don't see a way to hide the existence of cache lines etc. from the driver.
Best, Roland - 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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