[PATCH v4 1/7] dt-bindings: virtio-mmio: Add IOMMU description

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

The nature of a virtio-mmio node is discovered by the virtio driver at
probe time. However the DMA relation between devices must be described
statically. When a virtio-mmio node is a virtio-iommu device, it needs an
"#iommu-cells" property as specified by bindings/iommu/iommu.txt.

Otherwise, the virtio-mmio device may perform DMA through an IOMMU, which
requires an "iommus" property. Describe these requirements in the
device-tree bindings documentation.

Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Signed-off-by: Jean-Philippe Brucker <jean-philippe.brucker@arm.com>
---
 .../devicetree/bindings/virtio/mmio.txt       | 30 +++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/Documentation/devicetree/bindings/virtio/mmio.txt b/Documentation/devicetree/bindings/virtio/mmio.txt
index 5069c1b8e193..21af30fbb81f 100644
--- a/Documentation/devicetree/bindings/virtio/mmio.txt
+++ b/Documentation/devicetree/bindings/virtio/mmio.txt
@@ -8,10 +8,40 @@ 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 corresponds to a virtio-iommu device, it is
+		linked to DMA masters using the "iommus" or "iommu-map"
+		properties [1][2]. #iommu-cells specifies the size of the
+		"iommus" property. For virtio-iommu #iommu-cells must be
+		1, each cell describing a single endpoint ID.
+
+Optional properties:
+
+- iommus:	If the device accesses memory through an IOMMU, it should
+		have an "iommus" property [1]. Since virtio-iommu itself
+		does not access memory through an IOMMU, the "virtio,mmio"
+		node cannot have both an "#iommu-cells" and an "iommus"
+		property.
+
 Example:
 
 	virtio_block@3000 {
 		compatible = "virtio,mmio";
 		reg = <0x3000 0x100>;
 		interrupts = <41>;
+
+		/* Device has endpoint ID 23 */
+		iommus = <&viommu 23>
 	}
+
+	viommu: iommu@3100 {
+		compatible = "virtio,mmio";
+		reg = <0x3100 0x100>;
+		interrupts = <42>;
+
+		#iommu-cells = <1>
+	}
+
+[1] Documentation/devicetree/bindings/iommu/iommu.txt
+[2] Documentation/devicetree/bindings/pci/pci-iommu.txt
-- 
2.19.1