Hi Jean,
On 10/12/18 4:59 PM, Jean-Philippe Brucker wrote:
> 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.
>
> 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..748595473b36 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: virtio_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
>
Reviewed-by: Eric Auger <eric.auger@xxxxxxxxxx>
Thanks
Eric
