Messages in this thread | | | Date | Fri, 6 Sep 2013 15:14:44 +0100 | From | Catalin Marinas <> | Subject | Re: [PATCH v5 11/13] xen: introduce xen_alloc/free_coherent_pages |
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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
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