Am Dienstag, 16. Februar 2010 10:39:46 schrieb Russell King - ARM Linux: > However, because ARM CPUs can now speculatively prefetch, just leaving it > at that results in corruption of buffers used for DMA. So we have to > invalidate DMA_FROM_DEVICE and DMA_BIDIRECTIONAL buffers on unmap to > ensure coherency with DMA operations. > > If the CPU writes to a DMA_FROM_DEVICE buffer between map and unmap, the > writes can sit in the cache, and on unmap, they will be discarded. > > Cleaning the cache on unmap is not an option; that too can lead to DMA > buffer corruption in the DMA case. I am afraid for these controllers the controller driver must be responsible for all DMA and cache issues. Indicating the exact requirements to the upper layer would be a battle already lost. so the safe choice is not to set has_dma and the generic layer will leave the issue to the lower level. Regards Oliver -- 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
