On 2 April 2013 17:42, Paolo Bonzini <pbonz...@redhat.com> wrote: > Il 02/04/2013 18:10, Peter Maydell ha scritto: >> Aside: I may try to get rid of the DMAADDR property too at some >> point, because what the sysbus-ohci device should actually be doing >> is taking a MemoryRegion* [or maybe a DMAContext*] > > Avi had patches to unify DMAContext and MemoryRegion. I should revive > them perhaps.
Yes please. >> representing what >> it should be DMAing into, rather than the current "DMA into the >> system address space at addr + some constant offset" hack. One >> thing at a time, though. > > That's a general problem with sysbus. I guess if you need another > address space you should define your own bus, like PCI does. It's not a problem with sysbus, it's a problem with people being lazy about implementing things that do DMA. For instance PCI doesn't take a MemoryRegion* for DMA, it just assumes it can DMA into the system address space. (it does let you pass a DMAContext, but maybe that goes away with the patches you mention above; it's only used for spapr.) NB that "the PCI address space", ie the view of the world that the host controller sees when it makes a PCI access, is not the same as the address space that another bus mastering PCI device sees when it does a DMA access. Chances are good that the former shouldn't have any of the system's RAM in it and the latter should. (This is easy to handle though, you just create container MemoryRegions for each and pass them to the PCI code and make sure that you're using the right one at any particular point.) -- PMM
