linux/linux-5.4.31/Documentation/devicetree/bindings/pci/pci-iommu.txt

This document describes the generic device tree binding for describing the
relationship between PCI(e) devices and IOMMU(s).

Each PCI(e) device under a root complex is uniquely identified by its Requester
ID (AKA RID). A Requester ID is a triplet of a Bus number, Device number, and
Function number.

For the purpose of this document, when treated as a numeric value, a RID is
formatted such that:

* Bits [15:8] are the Bus number.
* Bits [7:3] are the Device number.
* Bits [2:0] are the Function number.
* Any other bits required for padding must be zero.

IOMMUs may distinguish PCI devices through sideband data derived from the
Requester ID. While a given PCI device can only master through one IOMMU, a
root complex may split masters across a set of IOMMUs (e.g. with one IOMMU per
bus).

The generic 'iommus' property is insufficient to describe this relationship,
and a mechanism is required to map from a PCI device to its IOMMU and sideband
data.

For generic IOMMU bindings, see
Documentation/devicetree/bindings/iommu/iommu.txt.


PCI root complex
================

Optional properties
-------------------

- iommu-map: Maps a Requester ID to an IOMMU and associated IOMMU specifier
  data.

  The property is an arbitrary number of tuples of
  (rid-base,iommu,iommu-base,length).

  Any RID r in the interval [rid-base, rid-base + length) is associated with
  the listed IOMMU, with the IOMMU specifier (r - rid-base + iommu-base).

- iommu-map-mask: A mask to be applied to each Requester ID prior to being
  mapped to an IOMMU specifier per the iommu-map property.


Example (1)
===========

/ {
	#address-cells = <1>;
	#size-cells = <1>;

	iommu: iommu@a {
		reg = <0xa 0x1>;
		compatible = "vendor,some-iommu";
		#iommu-cells = <1>;
	};

	pci: pci@f {
		reg = <0xf 0x1>;
		compatible = "vendor,pcie-root-complex";
		device_type = "pci";

		/*
		 * The sideband data provided to the IOMMU is the RID,
		 * identity-mapped.
		 */
		iommu-map = <0x0 &iommu 0x0 0x10000>;
	};
};


Example (2)
===========

/ {
	#address-cells = <1>;
	#size-cells = <1>;

	iommu: iommu@a {
		reg = <0xa 0x1>;
		compatible = "vendor,some-iommu";
		#iommu-cells = <1>;
	};

	pci: pci@f {
		reg = <0xf 0x1>;
		compatible = "vendor,pcie-root-complex";
		device_type = "pci";

		/*
		 * The sideband data provided to the IOMMU is the RID with the
		 * function bits masked out.
		 */
		iommu-map = <0x0 &iommu 0x0 0x10000>;
		iommu-map-mask = <0xfff8>;
	};
};


Example (3)
===========

/ {
	#address-cells = <1>;
	#size-cells = <1>;

	iommu: iommu@a {
		reg = <0xa 0x1>;
		compatible = "vendor,some-iommu";
		#iommu-cells = <1>;
	};

	pci: pci@f {
		reg = <0xf 0x1>;
		compatible = "vendor,pcie-root-complex";
		device_type = "pci";

		/*
		 * The sideband data provided to the IOMMU is the RID,
		 * but the high bits of the bus number are flipped.
		 */
		iommu-map = <0x0000 &iommu 0x8000 0x8000>,
			    <0x8000 &iommu 0x0000 0x8000>;
	};
};


Example (4)
===========

/ {
	#address-cells = <1>;
	#size-cells = <1>;

	iommu_a: iommu@a {
		reg = <0xa 0x1>;
		compatible = "vendor,some-iommu";
		#iommu-cells = <1>;
	};

	iommu_b: iommu@b {
		reg = <0xb 0x1>;
		compatible = "vendor,some-iommu";
		#iommu-cells = <1>;
	};

	iommu_c: iommu@c {
		reg = <0xc 0x1>;
		compatible = "vendor,some-iommu";
		#iommu-cells = <1>;
	};

	pci: pci@f {
		reg = <0xf 0x1>;
		compatible = "vendor,pcie-root-complex";
		device_type = "pci";

		/*
		 * Devices with bus number 0-127 are mastered via IOMMU
		 * a, with sideband data being RID[14:0].
		 * Devices with bus number 128-255 are mastered via
		 * IOMMU b, with sideband data being RID[14:0].
		 * No devices master via IOMMU c.
		 */
		iommu-map = <0x0000 &iommu_a 0x0000 0x8000>,
			    <0x8000 &iommu_b 0x0000 0x8000>;
	};
};