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? thanks -- PMM _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
