Docs: dt: Add PCI MSI map bindings

Currently msi-parent is used by a few bindings to describe the
relationship between a PCI root complex and a single MSI controller, but
this property does not have a generic binding document.

Additionally, msi-parent is insufficient to describe more complex
relationships between MSI controllers and devices under a root complex,
where devices may be able to target multiple MSI controllers, or where
MSI controllers use (non-probeable) sideband information to distinguish
devices.

This patch adds a generic binding for mapping PCI devices to MSI
controllers. This document covers msi-parent, and a new msi-map property
(specific to PCI*) which may be used to map devices (identified by their
Requester ID) to sideband data for each MSI controller that they may
target.

Acked-by: Marc Zyngier <[e-mail]>
Acked-by: Rob Herring <[e-mail]>
Signed-off-by: Mark Rutland <[e-mail]>
Signed-off-by: David Daney <[e-mail]>
Signed-off-by: Marc Zyngier <[e-mail]>

Documentation/devicetree/bindings/pci/pci-msi.txt

···
+This document describes the generic device tree binding for describing the
+relationship between PCI devices and MSI controllers.
+
+Each PCI 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.
+
+MSIs may be distinguished in part through the use of sideband data accompanying
+writes. In the case of PCI devices, this sideband data may be derived from the
+Requester ID. A mechanism is required to associate a device with both the MSI
+controllers it can address, and the sideband data that will be associated with
+its writes to those controllers.
+
+For generic MSI bindings, see
+Documentation/devicetree/bindings/interrupt-controller/msi.txt.
+
+
+PCI root complex
+================
+
+Optional properties
+-------------------
+
+- msi-map: Maps a Requester ID to an MSI controller and associated
+  msi-specifier data. The property is an arbitrary number of tuples of
+  (rid-base,msi-controller,msi-base,length), where:
+
+  * rid-base is a single cell describing the first RID matched by the entry.
+
+  * msi-controller is a single phandle to an MSI controller
+
+  * msi-base is an msi-specifier describing the msi-specifier produced for the
+    first RID matched by the entry.
+
+  * length is a single cell describing how many consecutive RIDs are matched
+    following the rid-base.
+
+  Any RID r in the interval [rid-base, rid-base + length) is associated with
+  the listed msi-controller, with the msi-specifier (r - rid-base + msi-base).
+
+- msi-map-mask: A mask to be applied to each Requester ID prior to being mapped
+  to an msi-specifier per the msi-map property.
+
+- msi-parent: Describes the MSI parent of the root complex itself. Where
+  the root complex and MSI controller do not pass sideband data with MSI
+  writes, this property may be used to describe the MSI controller(s)
+  used by PCI devices under the root complex, if defined as such in the
+  binding for the root complex.
+
+
+Example (1)
+===========
+
+/ {
+	#address-cells = <1>;
+	#size-cells = <1>;
+
+	msi: msi-controller@a {
+		reg = <0xa 0x1>;
+		compatible = "vendor,some-controller";
+		msi-controller;
+		#msi-cells = <1>;
+	};
+
+	pci: pci@f {
+		reg = <0xf 0x1>;
+		compatible = "vendor,pcie-root-complex";
+		device_type = "pci";
+
+		/*
+		 * The sideband data provided to the MSI controller is
+		 * the RID, identity-mapped.
+		 */
+		msi-map = <0x0 &msi_a 0x0 0x10000>,
+	};
+};
+
+
+Example (2)
+===========
+
+/ {
+	#address-cells = <1>;
+	#size-cells = <1>;
+
+	msi: msi-controller@a {
+		reg = <0xa 0x1>;
+		compatible = "vendor,some-controller";
+		msi-controller;
+		#msi-cells = <1>;
+	};
+
+	pci: pci@f {
+		reg = <0xf 0x1>;
+		compatible = "vendor,pcie-root-complex";
+		device_type = "pci";
+
+		/*
+		 * The sideband data provided to the MSI controller is
+		 * the RID, masked to only the device and function bits.
+		 */
+		msi-map = <0x0 &msi_a 0x0 0x100>,
+		msi-map-mask = <0xff>
+	};
+};
+
+
+Example (3)
+===========
+
+/ {
+	#address-cells = <1>;
+	#size-cells = <1>;
+
+	msi: msi-controller@a {
+		reg = <0xa 0x1>;
+		compatible = "vendor,some-controller";
+		msi-controller;
+		#msi-cells = <1>;
+	};
+
+	pci: pci@f {
+		reg = <0xf 0x1>;
+		compatible = "vendor,pcie-root-complex";
+		device_type = "pci";
+
+		/*
+		 * The sideband data provided to the MSI controller is
+		 * the RID, but the high bit of the bus number is
+		 * ignored.
+		 */
+		msi-map = <0x0000 &msi 0x0000 0x8000>,
+			  <0x8000 &msi 0x0000 0x8000>;
+	};
+};
+
+
+Example (4)
+===========
+
+/ {
+	#address-cells = <1>;
+	#size-cells = <1>;
+
+	msi: msi-controller@a {
+		reg = <0xa 0x1>;
+		compatible = "vendor,some-controller";
+		msi-controller;
+		#msi-cells = <1>;
+	};
+
+	pci: pci@f {
+		reg = <0xf 0x1>;
+		compatible = "vendor,pcie-root-complex";
+		device_type = "pci";
+
+		/*
+		 * The sideband data provided to the MSI controller is
+		 * the RID, but the high bit of the bus number is
+		 * negated.
+		 */
+		msi-map = <0x0000 &msi 0x8000 0x8000>,
+			  <0x8000 &msi 0x0000 0x8000>;
+	};
+};
+
+
+Example (5)
+===========
+
+/ {
+	#address-cells = <1>;
+	#size-cells = <1>;
+
+	msi_a: msi-controller@a {
+		reg = <0xa 0x1>;
+		compatible = "vendor,some-controller";
+		msi-controller;
+		#msi-cells = <1>;
+	};
+
+	msi_b: msi-controller@b {
+		reg = <0xb 0x1>;
+		compatible = "vendor,some-controller";
+		msi-controller;
+		#msi-cells = <1>;
+	};
+
+	msi_c: msi-controller@c {
+		reg = <0xc 0x1>;
+		compatible = "vendor,some-controller";
+		msi-controller;
+		#msi-cells = <1>;
+	};
+
+	pci: pci@c {
+		reg = <0xf 0x1>;
+		compatible = "vendor,pcie-root-complex";
+		device_type = "pci";
+
+		/*
+		 * The sideband data provided to MSI controller a is the
+		 * RID, but the high bit of the bus number is negated.
+		 * The sideband data provided to MSI controller b is the
+		 * RID, identity-mapped.
+		 * MSI controller c is not addressable.
+		 */
+		msi-map = <0x0000 &msi_a 0x8000 0x08000>,
+			  <0x8000 &msi_a 0x0000 0x08000>,
+			  <0x0000 &msi_b 0x0000 0x10000>;
+	};
+};