On Mon, Jun 27, 2016 at 02:15:29PM +0100, Peter Maydell wrote: > On 27 June 2016 at 10:47, Ard Biesheuvel <ard.biesheu...@linaro.org> wrote: > > As for the USB case, I can't really figure out what is going on here, > > but I am fairly certain it is a different issue. If this is related to > > DMA, I wonder if adding the 'dma-coherent' property to the PCIe root > > complex node fixes anything. > > 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. Thanks, Mark. [1] http://lists.infradead.org/pipermail/linux-arm-kernel/2016-June/433626.html [2] http://lists.infradead.org/pipermail/linux-arm-kernel/2016-June/434143.html _______________________________________________ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
