Messages in this thread | | | Date | Wed, 28 Aug 2013 21:07:52 +0100 | From | Stefano Stabellini <> | Subject | Re: [PATCH v4 10/10] xen/arm,arm64: enable SWIOTLB_XEN |
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On Thu, 15 Aug 2013, Ian Campbell wrote: > On Thu, 2013-08-15 at 12:10 +0100, Stefano Stabellini wrote: > > At the moment always rely on swiotlb-xen, but when Xen starts supporting > > hardware IOMMUs we'll be able to avoid it conditionally on the presence > > of an IOMMU on the platform. > > Do we have any idea how we are going to do this? > > It's extra complicated if you consider that on some systems on some of > the devices are behind an IOMMU :-/ > > I wonder if we can enumerate which devices have an IOMMU at boot time > and force a ludicrous dma mask (such as 0) if one isn't present in order > to force us to always take the exchange_and_pin path?
We don't need to worry about how to specify which devices need to go via the swiotlb internally, because we have our own arm specific dma_map_ops. At the moment they are just implemented using the swiotlb-xen functions, but we could easily provide wrappers that check our own internal whitelist/blacklist and go via swiotlb-xen only in those cases.
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