On Wed, 2015-10-28 at 16:40 +0900, Christian Borntraeger wrote: > Am 28.10.2015 um 16:17 schrieb Michael S. Tsirkin: > > On Tue, Oct 27, 2015 at 11:38:57PM -0700, Andy Lutomirski wrote: > > > This switches virtio to use the DMA API unconditionally. I'm sure > > > it breaks things, but it seems to work on x86 using virtio-pci, with > > > and without Xen, and using both the modern 1.0 variant and the > > > legacy variant. > > > > I'm very glad to see work on this making progress. > > > > I suspect we'll have to find a way to make this optional though, and > > keep doing the non-DMA API thing with old devices. And I've been > > debating with myself whether a pci specific thing or a feature bit is > > preferable. > > > > We have discussed that at kernel summit. I will try to implement a dummy > dma_ops for > s390 that does 1:1 mapping and Ben will look into doing some quirk to handle > "old" > code in addition to also make it possible to mark devices as iommu bypass > (IIRC, > via device tree, Ben?)
Right. You never eschew the DMA API in the *driver* — you just expect the DMA API to do the right thing for devices which don't need translation (with platforms using per-device dma_ops and generally getting their act together). We're pushing that on the platforms where it's currently an issue, including Power, SPARC and S390. -- dwmw2
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