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@xxxxxxxxxx>
Reviewed-by: Eric Auger <eric.auger@xxxxxxxxxx>
Signed-off-by: Jean-Philippe Brucker <jean-philippe.brucker@xxxxxxx>
---
.../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
--
2.21.0
