[PATCH v2 2/2] virtio: Document DMA coherency
From: Robin Murphy <robin.murphy@arm.com>
Date: 2017-02-02 16:36:21
Subsystem:
open firmware and flattened device tree bindings, the rest, virtio core · Maintainers:
Rob Herring, Krzysztof Kozlowski, Conor Dooley, Linus Torvalds, "Michael S. Tsirkin", Jason Wang
Possibly related (same subject, not in this thread)
- 2017-02-07 · Re: [PATCH v2 2/2] virtio: Document DMA coherency · Rob Herring <robh@kernel.org>
- 2017-02-03 · Re: [PATCH v2 2/2] virtio: Document DMA coherency · Will Deacon <hidden>
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@arm.com> --- 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; }
--
2.11.0.dirty