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+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>;
+ };
+};