On Mon, Feb 27, 2012 at 11:22:43AM +1100, David Gibson wrote: > On Sun, Feb 26, 2012 at 12:04:49PM +0200, Michael S. Tsirkin wrote: > > On Fri, Feb 24, 2012 at 02:27:39PM +1100, David Gibson wrote: > > > Not that long ago, every device implementation using DMA directly > > > accessed guest memory using cpu_physical_memory_*(). This meant that > > > adding support for a guest visible IOMMU would require changing every > > > one of these devices to go through IOMMU translation. > > > > > > Shortly before qemu 1.0, I made a start on fixing this by providing > > > helper functions for PCI DMA. These are currently just stubs which > > > call the direct access functions, but mean that an IOMMU can be > > > implemented in one place, rather than for every PCI device. > > > > > > Clearly, this doesn't help for non PCI devices, which could also be > > > IOMMU translated on some platforms. It is also problematic for the > > > devices which have both PCI and non-PCI version (e.g. OHCI, AHCI) - we > > > cannot use the the pci_dma_*() functions, because they assume the > > > presence of a PCIDevice, but we don't want to have to check between > > > pci_dma_*() and cpu_physical_memory_*() every time we do a DMA in the > > > device code. > > > > > > This patch makes the first step on addressing both these problems, by > > > introducing new (stub) dma helper functions which can be used for any > > > DMA capable device. > > > > > > These dma functions take a DMAContext *, a new (currently empty) > > > variable describing the DMA address space in which the operation is to > > > take place. NULL indicates untranslated DMA directly into guest > > > physical address space. The intention is that in future non-NULL > > > values will given information about any necessary IOMMU translation. > > > > > > DMA using devices must obtain a DMAContext (or, potentially, contexts) > > > from their bus or platform. For now this patch just converts the PCI > > > wrappers to be implemented in terms of the universal wrappers, > > > converting other drivers can take place over time. > > > > > > Cc: Michael S. Tsirkin <m...@redhat.com> > > > Cc: Joerg Rodel <joerg.ro...@amd.com> > > > Cc: Eduard - Gabriel Munteanu <eduard.munte...@linux360.ro> > > > Cc: Richard Henderson <r...@twiddle.net> > > > > > > Signed-off-by: David Gibson <da...@gibson.dropbear.id.au> > > > > I'm a bit confused with all the stubbing going on. > > Is this the final form of the pci_* functions or just > > a stub? If the final form, we probably should just > > open-code them - they don't buy us much. > > If not, let's add a comment? > > Well.. it's the intended final form of pci_dma_*() - which do become > trivial wrappers, yes.
I'd say let's drop them then (in a follow-up patch). The topic is confusing enough without having to wade through layers of wrappers :) > It's _not_ the intended final form of dma_*(), > which need to grow code to do actual IOMMU translation. I'll add a > comment about this in the next round. > > -- > David Gibson | I'll have my music baroque, and my code > david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ > _other_ > | _way_ _around_! > http://www.ozlabs.org/~dgibson
