dt-bindings: PCI: Add common schema for devices accessible through PCI BARs

Common YAML schema for devices that exports internal peripherals through
PCI BARs. The BARs are exposed as simple-buses through which the
peripherals can be accessed.

This is not intended to be used as a standalone binding, but should be
included by device specific bindings.

Signed-off-by: Andrea della Porta <andrea.porta@suse.com>
Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>
[bhelgaas: fix typo]
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Link: https://lore.kernel.org/r/096ab7addb39e498e28ac2526c07157cc9327c42.1742418429.git.andrea.porta@suse.com

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

@@ -0,0 +1,58 @@
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/pci/pci-ep-bus.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Common Properties for PCI MFD EP with Peripherals Addressable from BARs
+
+maintainers:
+  - A. della Porta  <andrea.porta@suse.com>
+
+description:
+  Define a generic node representing a PCI endpoint which contains several sub-
+  peripherals. The peripherals can be accessed through one or more BARs.
+  This common schema is intended to be referenced from device tree bindings and
+  does not represent a device tree binding by itself.
+
+properties:
+  '#address-cells':
+    const: 3
+
+  '#size-cells':
+    const: 2
+
+  ranges:
+    minItems: 1
+    maxItems: 6
+    items:
+      maxItems: 8
+      additionalItems: true
+      items:
+        - maximum: 5  # The BAR number
+        - const: 0
+        - const: 0
+
+patternProperties:
+  '^pci-ep-bus@[0-5]$':
+    type: object
+    description:
+      One node for each BAR used by peripherals contained in the PCI endpoint.
+      Each node represents a bus on which peripherals are connected.
+      This allows for some segmentation, e.g., one peripheral is accessible
+      through BAR0 and another through BAR1, and you don't want the two
+      peripherals to be able to act on the other BAR. Alternatively, when
+      different peripherals need to share BARs, you can define only one node
+      and use a 'ranges' property to map all the used BARs.
+
+    additionalProperties: true
+
+    properties:
+      compatible:
+        const: simple-bus
+
+    required:
+      - compatible
+
+additionalProperties: true
+...