Dear Rob On Mon, Mar 24, 2014 at 10:17 PM, Rob Herring <robherring2@xxxxxxxxx> wrote: > >>>> + dma_map_single(&ndev->dev, skb->data, >>>> + RX_BUF_SIZE, DMA_FROM_DEVICE); >>> >>> This is incorrect. >>> >>> buf = buffer alloc() >>> /* CPU owns buffer and can read/write it, device does not */ >>> dev_addr = dma_map_single(dev, buf, ..., DMA_FROM_DEVICE); >>> /* Device owns buffer and can write it, CPU does not access it */ >>> dma_unmap_single(dev, dev_addr, ..., DMA_FROM_DEVICE); >>> /* CPU owns buffer again and can read/write it, device does not */ >>> >>> Please turn on DMA API debugging in the kernel debug options and verify >>> whether your driver causes it to complain (it will.) >> >> Yes, you are right. >> After change to dma_map/unmap_single, however, still get warning like >> "DMA-API: device driver failed to check map error", not sure whether >> it can be ignored? > > If it could be ignored, there would be no warning. So yes you should > check the error. I guess correct error handling would be throwing away > the packet. The warning is solved via adding dma_mapping_error check after every dma_map_single. > > >>>> + dma_map_single(&ndev->dev, buf, RX_BUF_SIZE, DMA_TO_DEVICE); >>>> + hip04_set_recv_desc(priv, virt_to_phys(buf)); >>> >>> No need for virt_to_phys() here - dma_map_single() returns the device >>> address. >> Got it. >> Use virt_to_phys since find same result come out, it should be >> different for iommu case. >> >> In fact, the hardware can help to do the cache flushing, the function >> still not be enabled now. >> Then dma_map/unmap_single may be ignored. > > If you don't need cache flushing, you should setup different > dma_map_ops for the device such as arm_coherent_dma_ops. The driver > should always have the dma_map calls. See highbank and mvebu for > examples. That would be very helpful, still not sure how to enable this feature. Could you help clarify which file. Not find highbank and mvebu under drivers/iommu/. Thanks -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
