Re: [PATCH v8 2/7] dt-bindings: virtio: Add virtio-pci-iommu node

["Michael S. Tsirkin" <mst@redhat.com>]

On Thu, May 30, 2019 at 06:09:24PM +0100, Jean-Philippe Brucker wrote:
> Some systems implement virtio-iommu as a PCI endpoint. The operating
> system needs to discover the relationship between IOMMU and masters long
> before the PCI endpoint gets probed. Add a PCI child node to describe the
> virtio-iommu device.
> 
> The virtio-pci-iommu is conceptually split between a PCI programming
> interface and a translation component on the parent bus. The latter
> doesn't have a node in the device tree. The virtio-pci-iommu node
> describes both, by linking the PCI endpoint to "iommus" property of DMA
> master nodes and to "iommu-map" properties of bus nodes.
> 
> 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>

So this is just an example right?
We are not defining any new properties or anything like that.

I think down the road for non dt platforms we want to put this
info in the config space of the device. I do not think ACPI
is the best option for this since not all systems have it.
But that can wait.

> ---
>  .../devicetree/bindings/virtio/iommu.txt      | 66 +++++++++++++++++++
>  1 file changed, 66 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/virtio/iommu.txt
> 
> diff --git a/Documentation/devicetree/bindings/virtio/iommu.txt b/Documentation/devicetree/bindings/virtio/iommu.txt
> new file mode 100644
> index 000000000000..2407fea0651c
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/virtio/iommu.txt
> @@ -0,0 +1,66 @@
> +* virtio IOMMU PCI device
> +
> +When virtio-iommu uses the PCI transport, its programming interface is
> +discovered dynamically by the PCI probing infrastructure. However the
> +device tree statically describes the relation between IOMMU and DMA
> +masters. Therefore, the PCI root complex that hosts the virtio-iommu
> +contains a child node representing the IOMMU device explicitly.
> +
> +Required properties:
> +
> +- compatible:	Should be "virtio,pci-iommu"
> +- reg:		PCI address of the IOMMU. As defined in the PCI Bus
> +		Binding reference [1], the reg property is a five-cell
> +		address encoded as (phys.hi phys.mid phys.lo size.hi
> +		size.lo). phys.hi should contain the device's BDF as
> +		0b00000000 bbbbbbbb dddddfff 00000000. The other cells
> +		should be zero.
> +- #iommu-cells:	Each platform DMA master managed by the IOMMU is assigned
> +		an endpoint ID, described by the "iommus" property [2].
> +		For virtio-iommu, #iommu-cells must be 1.
> +
> +Notes:
> +
> +- DMA from the IOMMU device isn't managed by another IOMMU. Therefore the
> +  virtio-iommu node doesn't have an "iommus" property, and is omitted from
> +  the iommu-map property of the root complex.
> +
> +Example:
> +
> +pcie@10000000 {
> +	compatible = "pci-host-ecam-generic";
> +	...
> +
> +	/* The IOMMU programming interface uses slot 00:01.0 */
> +	iommu0: iommu@0008 {
> +		compatible = "virtio,pci-iommu";
> +		reg = <0x00000800 0 0 0 0>;
> +		#iommu-cells = <1>;
> +	};
> +
> +	/*
> +	 * The IOMMU manages all functions in this PCI domain except
> +	 * itself. Omit BDF 00:01.0.
> +	 */
> +	iommu-map = <0x0 &iommu0 0x0 0x8>
> +		    <0x9 &iommu0 0x9 0xfff7>;
> +};
> +
> +pcie@20000000 {
> +	compatible = "pci-host-ecam-generic";
> +	...
> +	/*
> +	 * The IOMMU also manages all functions from this domain,
> +	 * with endpoint IDs 0x10000 - 0x1ffff
> +	 */
> +	iommu-map = <0x0 &iommu0 0x10000 0x10000>;
> +};
> +
> +ethernet@fe001000 {
> +	...
> +	/* The IOMMU manages this platform device with endpoint ID 0x20000 */
> +	iommus = <&iommu0 0x20000>;
> +};
> +
> +[1] Documentation/devicetree/bindings/pci/pci.txt
> +[2] Documentation/devicetree/bindings/iommu/iommu.txt
> -- 
> 2.21.0
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