dt-bindings: PCI: pci-ep: Add support for iommu-map and msi-map

Document the use of (msi|iommu)-map for PCI Endpoint (EP) controllers,
which can use MSI as a doorbell mechanism. Each EP controller can support
up to 8 physical functions and 65,536 virtual functions.

Define how to construct device IDs using function bits [2:0] and virtual
function index bits [31:3], enabling (msi|iommu)-map to associate each
child device with a specific (msi|iommu)-specifier.

The EP cannot rely on PCI Requester ID (RID) because the RID is determined
by the PCI topology of the host system. Since the EP may be connected to
different PCI hosts, the RID can vary between systems and is therefore not
a reliable identifier.

Signed-off-by: Frank Li <Frank.Li@nxp.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Link: https://lore.kernel.org/all/20250414-ep-msi-v18-4-f69b49917464@nxp.com

Documentation/devicetree/bindings/pci/pci-ep.yaml

@@ -17,6 +17,24 @@ properties:
   $nodename:
     pattern: "^pcie-ep@"
 
+  iommu-map:
+    $ref: /schemas/types.yaml#/definitions/uint32-matrix
+    items:
+      items:
+        - description: Device ID (see msi-map) base
+          maximum: 0x7ffff
+        - description: phandle to IOMMU
+        - description: IOMMU specifier base (currently always 1 cell)
+        - description: Number of Device IDs
+          maximum: 0x80000
+
+  iommu-map-mask:
+    description:
+      A mask to be applied to each Device ID prior to being mapped to an
+      IOMMU specifier per the iommu-map property.
+    $ref: /schemas/types.yaml#/definitions/uint32
+    maximum: 0x7ffff
+
   max-functions:
     description: Maximum number of functions that can be configured
     $ref: /schemas/types.yaml#/definitions/uint8
@@ -35,6 +53,56 @@ properties:
     $ref: /schemas/types.yaml#/definitions/uint32
     enum: [ 1, 2, 3, 4 ]
 
+  msi-map:
+    description: |
+      Maps a Device ID to an MSI and associated MSI specifier data.
+
+      A PCI Endpoint (EP) can use MSI as a doorbell function. This is achieved by
+      mapping the MSI controller's address into PCI BAR<n>. The PCI Root Complex
+      can write to this BAR<n>, triggering the EP to generate IRQ. This notifies
+      the EP-side driver of an event, eliminating the need for the driver to
+      continuously poll for status changes.
+
+      However, the EP cannot rely on Requester ID (RID) because the RID is
+      determined by the PCI topology of the host system. Since the EP may be
+      connected to different PCI hosts, the RID can vary between systems and is
+      therefore not a reliable identifier.
+
+      Each EP can support up to 8 physical functions and up to 65,536 virtual
+      functions. To uniquely identify each child device, a device ID is defined
+      as
+         - Bits [2:0] for the function number (func)
+         - Bits [18:3] for the virtual function index (vfunc)
+
+      The resulting device ID is computed as:
+
+        (func & 0x7) | (vfunc << 3)
+
+      The property is an arbitrary number of tuples of
+      (device-id-base, msi, msi-base,length).
+
+      Any Device ID id in the interval [id-base, id-base + length) is
+      associated with the listed MSI, with the MSI specifier
+      (id - id-base + msi-base).
+    $ref: /schemas/types.yaml#/definitions/uint32-matrix
+    items:
+      items:
+        - description: The Device ID base matched by the entry
+          maximum: 0x7ffff
+        - description: phandle to msi-controller node
+        - description: (optional) The msi-specifier produced for the first
+            Device ID matched by the entry. Currently, msi-specifier is 0 or
+            1 cells.
+        - description: The length of consecutive Device IDs following the
+            Device ID base
+          maximum: 0x80000
+
+  msi-map-mask:
+    description: A mask to be applied to each Device ID prior to being
+      mapped to an msi-specifier per the msi-map property.
+    $ref: /schemas/types.yaml#/definitions/uint32
+    maximum: 0x7ffff
+
   num-lanes:
     description: maximum number of lanes
     $ref: /schemas/types.yaml#/definitions/uint32