linux-arkmicro/linux/Documentation/devicetree/bindings/power/power_domain.txt

* Generic PM domains

System on chip designs are often divided into multiple PM domains that can be
used for power gating of selected IP blocks for power saving by reduced leakage
current.

This device tree binding can be used to bind PM domain consumer devices with
their PM domains provided by PM domain providers. A PM domain provider can be
represented by any node in the device tree and can provide one or more PM
domains. A consumer node can refer to the provider by a phandle and a set of
phandle arguments (so called PM domain specifiers) of length specified by the
#power-domain-cells property in the PM domain provider node.

==PM domain providers==

Required properties:
 - #power-domain-cells : Number of cells in a PM domain specifier;
   Typically 0 for nodes representing a single PM domain and 1 for nodes
   providing multiple PM domains (e.g. power controllers), but can be any value
   as specified by device tree binding documentation of particular provider.

Optional properties:
 - power-domains : A phandle and PM domain specifier as defined by bindings of
                   the power controller specified by phandle.
   Some power domains might be powered from another power domain (or have
   other hardware specific dependencies). For representing such dependency
   a standard PM domain consumer binding is used. When provided, all domains
   created by the given provider should be subdomains of the domain
   specified by this binding. More details about power domain specifier are
   available in the next section.

- domain-idle-states : A phandle of an idle-state that shall be soaked into a
                generic domain power state. The idle state definitions are
                compatible with domain-idle-state specified in [1]. phandles
                that are not compatible with domain-idle-state will be
                ignored.
  The domain-idle-state property reflects the idle state of this PM domain and
  not the idle states of the devices or sub-domains in the PM domain. Devices
  and sub-domains have their own idle-states independent of the parent
  domain's idle states. In the absence of this property, the domain would be
  considered as capable of being powered-on or powered-off.

- operating-points-v2 : Phandles to the OPP tables of power domains provided by
  a power domain provider. If the provider provides a single power domain only
  or all the power domains provided by the provider have identical OPP tables,
  then this shall contain a single phandle. Refer to ../opp/opp.txt for more
  information.

Example:

	power: power-controller@12340000 {
		compatible = "foo,power-controller";
		reg = <0x12340000 0x1000>;
		#power-domain-cells = <1>;
	};

The node above defines a power controller that is a PM domain provider and
expects one cell as its phandle argument.

Example 2:

	parent: power-controller@12340000 {
		compatible = "foo,power-controller";
		reg = <0x12340000 0x1000>;
		#power-domain-cells = <1>;
	};

	child: power-controller@12341000 {
		compatible = "foo,power-controller";
		reg = <0x12341000 0x1000>;
		power-domains = <&parent 0>;
		#power-domain-cells = <1>;
	};

The nodes above define two power controllers: 'parent' and 'child'.
Domains created by the 'child' power controller are subdomains of '0' power
domain provided by the 'parent' power controller.

Example 3:
	parent: power-controller@12340000 {
		compatible = "foo,power-controller";
		reg = <0x12340000 0x1000>;
		#power-domain-cells = <0>;
		domain-idle-states = <&DOMAIN_RET>, <&DOMAIN_PWR_DN>;
	};

	child: power-controller@12341000 {
		compatible = "foo,power-controller";
		reg = <0x12341000 0x1000>;
		power-domains = <&parent>;
		#power-domain-cells = <0>;
		domain-idle-states = <&DOMAIN_PWR_DN>;
	};

	DOMAIN_RET: state@0 {
		compatible = "domain-idle-state";
		reg = <0x0>;
		entry-latency-us = <1000>;
		exit-latency-us = <2000>;
		min-residency-us = <10000>;
	};

	DOMAIN_PWR_DN: state@1 {
		compatible = "domain-idle-state";
		reg = <0x1>;
		entry-latency-us = <5000>;
		exit-latency-us = <8000>;
		min-residency-us = <7000>;
	};

==PM domain consumers==

Required properties:
 - power-domains : A list of PM domain specifiers, as defined by bindings of
		the power controller that is the PM domain provider.

Optional properties:
 - power-domain-names : A list of power domain name strings sorted in the same
		order as the power-domains property. Consumers drivers will use
		power-domain-names to match power domains with power-domains
		specifiers.

Example:

	leaky-device@12350000 {
		compatible = "foo,i-leak-current";
		reg = <0x12350000 0x1000>;
		power-domains = <&power 0>;
		power-domain-names = "io";
	};

	leaky-device@12351000 {
		compatible = "foo,i-leak-current";
		reg = <0x12351000 0x1000>;
		power-domains = <&power 0>, <&power 1> ;
		power-domain-names = "io", "clk";
	};

The first example above defines a typical PM domain consumer device, which is
located inside a PM domain with index 0 of a power controller represented by a
node with the label "power".
In the second example the consumer device are partitioned across two PM domains,
the first with index 0 and the second with index 1, of a power controller that
is represented by a node with the label "power".

Optional properties:
- required-opps: This contains phandle to an OPP node in another device's OPP
  table. It may contain an array of phandles, where each phandle points to an
  OPP of a different device. It should not contain multiple phandles to the OPP
  nodes in the same OPP table. This specifies the minimum required OPP of the
  device(s), whose OPP's phandle is present in this property, for the
  functioning of the current device at the current OPP (where this property is
  present).

Example:
- OPP table for domain provider that provides two domains.

	domain0_opp_table: opp-table0 {
		compatible = "operating-points-v2";

		domain0_opp_0: opp-1000000000 {
			opp-hz = /bits/ 64 <1000000000>;
			opp-microvolt = <975000 970000 985000>;
		};
		domain0_opp_1: opp-1100000000 {
			opp-hz = /bits/ 64 <1100000000>;
			opp-microvolt = <1000000 980000 1010000>;
		};
	};

	domain1_opp_table: opp-table1 {
		compatible = "operating-points-v2";

		domain1_opp_0: opp-1200000000 {
			opp-hz = /bits/ 64 <1200000000>;
			opp-microvolt = <975000 970000 985000>;
		};
		domain1_opp_1: opp-1300000000 {
			opp-hz = /bits/ 64 <1300000000>;
			opp-microvolt = <1000000 980000 1010000>;
		};
	};

	power: power-controller@12340000 {
		compatible = "foo,power-controller";
		reg = <0x12340000 0x1000>;
		#power-domain-cells = <1>;
		operating-points-v2 = <&domain0_opp_table>, <&domain1_opp_table>;
	};

	leaky-device0@12350000 {
		compatible = "foo,i-leak-current";
		reg = <0x12350000 0x1000>;
		power-domains = <&power 0>;
		required-opps = <&domain0_opp_0>;
	};

	leaky-device1@12350000 {
		compatible = "foo,i-leak-current";
		reg = <0x12350000 0x1000>;
		power-domains = <&power 1>;
		required-opps = <&domain1_opp_1>;
	};

[1]. Documentation/devicetree/bindings/power/domain-idle-state.txt