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dt-bindings: virtio-mmio: Add IOMMU description

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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>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
This commit is contained in:
Jean-Philippe Brucker 2019-01-15 12:19:53 +00:00 committed by Michael S. Tsirkin
parent 0b4a7092ff
commit 8447d84e35
1 changed files with 30 additions and 0 deletions
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30
Documentation/devicetree/bindings/virtio/mmio.txt
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@ -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