dt-bindings: power: Add apple,pmgr-pwrstate binding

This syscon child node represents a single SoC device controlled by the
PMGR block. This layout allows us to declare all device power state
controls (power/clock gating and reset) in the device tree, including
dependencies, instead of hardcoding it into the driver. The register
layout is uniform.

Each pmgr-pwrstate node provides genpd and reset features, to be
consumed by downstream device nodes.

Future SoCs are expected to use backwards compatible registers, and the
"apple,pmgr-pwrstate" represents any such interfaces (possibly with
additional features gated by the more specific compatible), allowing
them to be bound without driver updates. If a backwards incompatible
change is introduced in future SoCs, it will require a new compatible,
such as "apple,pmgr-pwrstate-v2".

Reviewed-by: Mark Kettenis <kettenis@openbsd.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Hector Martin <marcan@marcan.st>

Documentation/devicetree/bindings/power/apple,pmgr-pwrstate.yaml

@@ -0,0 +1,71 @@
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/power/apple,pmgr-pwrstate.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Apple SoC PMGR Power States
+
+maintainers:
+  - Hector Martin <marcan@marcan.st>
+
+allOf:
+  - $ref: "power-domain.yaml#"
+
+description: |
+  Apple SoCs include PMGR blocks responsible for power management,
+  which can control various clocks, resets, power states, and
+  performance features. This binding describes the device power
+  state registers, which control power states and resets.
+
+  Each instance of a power controller within the PMGR syscon node
+  represents a generic power domain provider, as documented in
+  Documentation/devicetree/bindings/power/power-domain.yaml.
+  The provider controls a single SoC block. The power hierarchy is
+  represented via power-domains relationships between these nodes.
+
+  See Documentation/devicetree/bindings/arm/apple/apple,pmgr.yaml
+  for the top-level PMGR node documentation.
+
+properties:
+  compatible:
+    items:
+      - enum:
+          - apple,t8103-pmgr-pwrstate
+          - apple,t6000-pmgr-pwrstate
+      - const: apple,pmgr-pwrstate
+
+  reg:
+    maxItems: 1
+
+  "#power-domain-cells":
+    const: 0
+
+  "#reset-cells":
+    const: 0
+
+  power-domains:
+    description:
+      Reference to parent power domains. A domain may have multiple parents,
+      and all will be powered up when it is powered.
+    minItems: 1
+    maxItems: 8 # Arbitrary, should be enough
+
+  label:
+    description:
+      Specifies the name of the SoC domain being controlled. This is used to
+      name the power/reset domains.
+
+  apple,always-on:
+    description:
+      Forces this power domain to always be powered up.
+    type: boolean
+
+required:
+  - compatible
+  - reg
+  - "#power-domain-cells"
+  - "#reset-cells"
+  - label
+
+additionalProperties: false