[PATCH v2 1/5] dt-bindings: virtio: Specify #iommu-cells value for a virtio-iommu

[Jean-Philippe Brucker <jean-philippe.brucker@arm.com>]

A virtio-mmio node may represent a virtio-iommu device. This is discovered
by the virtio driver at probe time, but the DMA topology isn't
discoverable and must be described by firmware. For DT the standard IOMMU
description is used, as specified in bindings/iommu/iommu.txt and
bindings/pci/pci-iommu.txt. Like many other IOMMUs, virtio-iommu
distinguishes masters by their endpoint IDs, which requires one IOMMU cell
in the "iommus" property.

Signed-off-by: Jean-Philippe Brucker <jean-philippe.brucker@arm.com>
---
 Documentation/devicetree/bindings/virtio/mmio.txt | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/Documentation/devicetree/bindings/virtio/mmio.txt b/Documentation/devicetree/bindings/virtio/mmio.txt
index 5069c1b8e193..337da0e3a87f 100644
--- a/Documentation/devicetree/bindings/virtio/mmio.txt
+++ b/Documentation/devicetree/bindings/virtio/mmio.txt
@@ -8,6 +8,14 @@ Required properties:
 - reg:		control registers base address and size including configuration space
 - interrupts:	interrupt generated by the device
 
+Required properties for virtio-iommu:
+
+- #iommu-cells:	When the node describes a virtio-iommu device, it is
+		linked to DMA masters using the "iommus" property as
+		described in devicetree/bindings/iommu/iommu.txt. For
+		virtio-iommu #iommu-cells must be 1, each cell describing
+		a single endpoint ID.
+
 Example:
 
 	virtio_block@3000 {
-- 
2.17.0