Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> writes: >> >> The fix is to use usb_buffer_alloc() for that purpose which ensures >> memory that is suitable for DMA. And on x86_64, this also means that the >> upper 32 bits of the address returned are all 0's. > > That is not a good fix. usb_buffer_alloc() provides coherent memory, > which is not what we want. I believe the correct fix is to specify the > GFP_DMA32 flag in the kzalloc() call. The traditional way to handle this is to leave it to swiotlb in pci_map_*. pci_map_* is needed anyways if you run with a IOMMU. Also note at least on x86 systems coherent memory is the same as non coherent memory. And GFP_DMA32 is a x86 specific flag, doesn't necessarily do any good anywhere else. So if you add x86isms anyways you could as well use dma_alloc_coherent() directly which is actually better at this than a simple GFP_DMA32 and as a bonus handles the IOMMUs correctly too. Or just use GFP_KERNEL and pci_map_* later. -Andi -- ak@xxxxxxxxxxxxxxx -- Speaking for myself only. -- 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
