On Wed, 2010-02-17 at 09:55 +0000, Russell King - ARM Linux wrote: > Nope. It's to do with mapping a buffer for DMA, and then doing PIO > reads/writes to it. > > With speculative prefetches, you have to deal with cache coherency with > hardware DMA on DMA unmap. If you've written to the buffer in violation > of the DMA API buffer ownership rules, then your writes get thrown away > resulting in immediate data corruption. Right, and this exact same problem will bite some embedded powerpc too I suppose :-) Hrm... actually not :-) We don't do the invalidate at unmap time today because we know 44x have such a broken prefetcher that we disable it ... interesting considering that there are machines around that do non-coherent DMA with 750's style chips who -do- have a prefetcher... damn, we have a bug :-) In any case, same problem here. See my reply to Oliver. Basically, the problem boils down to the dma_map/unmap being done at the wrong layer. The driver should simply not do these if it's going to do PIO over that range. Cheers, Ben. -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
