On Thu, Sep 05, 2013 at 05:43:33PM +0100, Stefano Stabellini wrote: > On Thu, 5 Sep 2013, Catalin Marinas wrote: > > On Thu, Aug 29, 2013 at 07:32:32PM +0100, Stefano Stabellini wrote: > > > xen_swiotlb_alloc_coherent needs to allocate a coherent buffer for cpu > > > and devices. On native x86 and ARMv8 is sufficient to call > > > __get_free_pages in order to get a coherent buffer, while on ARM we need > > > to call arm_dma_ops.alloc. > > > > Don't bet on this for ARMv8. It's not mandated for the architecture, so > > at some point some SoC will require non-cacheable buffers for coherency. > > I see. > Would it be better if I implemented xen_alloc_coherent_pages on armv8 by > calling arm64_swiotlb_dma_ops.alloc?
What does this buffer do exactly? Is it allocated by guests? Currently arm64_swiotlb_dma_ops assume cache-coherent DMA. I have a patch which introduces new ops for non-coherent DMA but this should really be orthogonal to swiotlb. You can basically have 4 combinations of coherent/non-coherent and swiotlb/iommu. Mark Rutland is currently looking into how best to describe this via DT as it may not even be per SoC but per bus or device. -- Catalin -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
