On Mon, Jun 27, 2016 at 03:10:20PM +0100, Peter Maydell wrote: > On 27 June 2016 at 14:49, Mark Rutland <mark.rutland@xxxxxxx> wrote: > > On Mon, Jun 27, 2016 at 02:15:29PM +0100, Peter Maydell wrote: > >> I get the impression dma-coherent is the right thing to advertise > >> anyway. Do you have the documentation to hand that specifies what > >> "dma-coherent" means? The Documentation/devicetree docs in the > >> kernel tree seem to rather unhelpfully define it as "Present if > >> dma operations are coherent", which doesn't really clarify anything > >> to me... > > > > It's ill-defined today, and the precise definition is an open question. > > See replies to [1], which seems to have stalled as of [2]. > > > > My view is that for arm/arm64 this should mean the device makes accesses > > which are coherent with Inner Shareable Normal Inner-WB Outer-WB > > attributes, as this is the functional de-facto semantics today, and > > anything short of that is not well-defined or usable. > > OK, so for any emulated device in QEMU we should specify > dma-coherent by those rules. I think our only DMA devices > in the virt board are the emulated PCI devices; dma-coherent > here is a property of the pci-controller and applies to any > device on it, right? Presumably this means that if the host > pci-controller doesn't advertise itself as dma-coherent then > we cannot do any PCI passthrough of host hardware? > Someone suggested a while back to have a second PCI controller matching the host properties for this purpose... -Christoffer _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
