dt-bindings: document generic access controllers

Introducing of the generic access controllers bindings for the
access controller provider and consumer devices. Those bindings are
intended to allow a better handling of accesses to resources in a
hardware architecture supporting several compartments.

This patch is based on [1]. It is integrated in this patchset as it
provides a use-case for it.

Diffs with [1]:
- Rename feature-domain* properties to access-control* to narrow
down the scope of the binding
- YAML errors and typos corrected.
- Example updated
- Some rephrasing in the binding description

[1]: https://lore.kernel.org/lkml/0c0a82bb-18ae-d057-562b

Signed-off-by: Oleksii Moisieiev <[e-mail]>
Signed-off-by: Gatien Chevallier <[e-mail]>
Reviewed-by: Rob Herring <[e-mail]>
Signed-off-by: Alexandre Torgue <[e-mail]>

Documentation/devicetree/bindings/access-controllers/access-controllers.yaml

···
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/access-controllers/access-controllers.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Generic Domain Access Controllers
+
+maintainers:
+  - Oleksii Moisieiev <[e-mail]>
+
+description: |+
+  Common access controllers properties
+
+  Access controllers are in charge of stating which of the hardware blocks under
+  their responsibility (their domain) can be accesssed by which compartment. A
+  compartment can be a cluster of CPUs (or coprocessors), a range of addresses
+  or a group of hardware blocks. An access controller's domain is the set of
+  resources covered by the access controller.
+
+  This device tree binding can be used to bind devices to their access
+  controller provided by access-controllers property. In this case, the device
+  is a consumer and the access controller is the provider.
+
+  An access controller can be represented by any node in the device tree and
+  can provide one or more configuration parameters, needed to control parameters
+  of the consumer device. A consumer node can refer to the provider by phandle
+  and a set of phandle arguments, specified by '#access-controller-cells'
+  property in the access controller node.
+
+  Access controllers are typically used to set/read the permissions of a
+  hardware block and grant access to it. Any of which depends on the access
+  controller. The capabilities of each access controller are defined by the
+  binding of the access controller device.
+
+  Each node can be a consumer for the several access controllers.
+
+# always select the core schema
+select: true
+
+properties:
+  "#access-controller-cells":
+    description:
+      Number of cells in an access-controllers specifier;
+      Can be any value as specified by device tree binding documentation
+      of a particular provider. The node is an access controller.
+
+  access-controller-names:
+    $ref: /schemas/types.yaml#/definitions/string-array
+    description:
+      A list of access-controllers names, sorted in the same order as
+      access-controllers entries. Consumer drivers will use
+      access-controller-names to match with existing access-controllers entries.
+
+  access-controllers:
+    $ref: /schemas/types.yaml#/definitions/phandle-array
+    description:
+      A list of access controller specifiers, as defined by the
+      bindings of the access-controllers provider.
+
+additionalProperties: true
+
+examples:
+  - |
+    clock_controller: access-controllers@50000 {
+        reg = <0x50000 0x400>;
+        #access-controller-cells = <2>;
+    };
+
+    bus_controller: bus@60000 {
+        reg = <0x60000 0x10000>;
+        #address-cells = <1>;
+        #size-cells = <1>;
+        ranges;
+        #access-controller-cells = <3>;
+
+        uart4: serial@60100 {
+            reg = <0x60100 0x400>;
+            clocks = <&clk_serial>;
+            access-controllers = <&clock_controller 1 2>,
+                                 <&bus_controller 1 3 5>;
+            access-controller-names = "clock", "bus";
+        };
+    };