On Thu, Feb 02, 2017 at 04:36:21PM +0000, Robin Murphy wrote: > Since making use of the DMA API will require the architecture code to > have the correct notion of device cache-coherency on architectures like > ARM, explicitly call this out in the virtio-mmio DT binding. The ship > has sailed for legacy virtio, but let's hope that we can head off any > future firmware mishaps. > > Signed-off-by: Robin Murphy <robin.murphy@xxxxxxx> > --- > Documentation/devicetree/bindings/virtio/mmio.txt | 11 +++++++++++ > 1 file changed, 11 insertions(+) > > diff --git a/Documentation/devicetree/bindings/virtio/mmio.txt b/Documentation/devicetree/bindings/virtio/mmio.txt > index 5069c1b8e193..999a93faa67c 100644 > --- a/Documentation/devicetree/bindings/virtio/mmio.txt > +++ b/Documentation/devicetree/bindings/virtio/mmio.txt > @@ -7,6 +7,16 @@ Required properties: > - compatible: "virtio,mmio" compatibility string > - reg: control registers base address and size including configuration space > - interrupts: interrupt generated by the device > +- dma-coherent: required if the device (or host emulation) accesses memory > + cache-coherently, absent otherwise > + > +Linux implementation note: > + > +virtio devices not advertising the VIRTIO_F_IOMMU_PLATFORM flag have been > +implicitly assumed to be cache-coherent by Linux, and for legacy reasons this > +behaviour is likely to remain. If VIRTIO_F_IOMMU_PLATFORM is advertised, then > +such assumptions cannot be relied upon and the "dma-coherent" property must > +accurately reflect the coherency of the device. > > Example: > > @@ -14,4 +24,5 @@ Example: > compatible = "virtio,mmio"; > reg = <0x3000 0x100>; > interrupts = <41>; > + dma-coherent; I think this is a sensible update to the binding and is independent of whatever we decide to do for IOMMUs and DMA on legacy devices. Acked-by: Will Deacon <will.deacon@xxxxxxx> Will -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
