[PATCH v10 05/27] dt: psci: Update DT bindings to support hierarchical PSCI states

[Ulf Hansson]

From: Lina Iyer <lina.iyer@xxxxxxxxxx>

Update DT bindings to represent hierarchical CPU and CPU PM domain idle
states for PSCI. Also update the PSCI examples to clearly show how
flattened and hierarchical idle states can be represented in DT.

Cc: Lina Iyer <ilina@xxxxxxxxxxxxxx>
Signed-off-by: Lina Iyer <lina.iyer@xxxxxxxxxx>
Co-developed-by: Ulf Hansson <ulf.hansson@xxxxxxxxxx>
Signed-off-by: Ulf Hansson <ulf.hansson@xxxxxxxxxx>
Reviewed-by: Rob Herring <robh@xxxxxxxxxx>
Reviewed-by: Sudeep Holla <sudeep.holla@xxxxxxx>
---

Change in V10:
	- Clarified that the new hierarchical representation is orthogonal to
	  OS-initiated vs platform-coordinated PSCI CPU suspend mode.
	- Clarified the representation for "arm,psci-suspend-param" in regards
	  to the flattened vs hierarchical model.
	- Added power-domain-names property to the CPU nodes, as to avoid
	  future churns, if ever multiple power-domains specifiers.

---
 .../devicetree/bindings/arm/psci.txt          | 166 ++++++++++++++++++
 1 file changed, 166 insertions(+)

diff --git a/Documentation/devicetree/bindings/arm/psci.txt b/Documentation/devicetree/bindings/arm/psci.txt
index a2c4f1d52492..e6d3553c8df8 100644
--- a/Documentation/devicetree/bindings/arm/psci.txt
+++ b/Documentation/devicetree/bindings/arm/psci.txt
@@ -105,7 +105,173 @@ Case 3: PSCI v0.2 and PSCI v0.1.
 		...
 	};
 
+ARM systems can have multiple cores sometimes in hierarchical arrangement.
+This often, but not always, maps directly to the processor power topology of
+the system. Individual nodes in a topology have their own specific power states
+and can be better represented in DT hierarchically.
+
+For these cases, the definitions of the idle states for the CPUs and the CPU
+topology, must conform to the domain idle state specification [3]. The domain
+idle states themselves, must be compatible with the defined 'domain-idle-state'
+binding [1], and also need to specify the arm,psci-suspend-param property for
+each idle state.
+
+DT allows representing CPUs and CPU idle states in two different ways -
+
+The flattened model as given in Example 1, lists CPU's idle states followed by
+the domain idle state that the CPUs may choose. Note that the idle states are
+all compatible with "arm,idle-state". Additionally, for the domain idle state
+the "arm,psci-suspend-param" represents a superset of the CPU's idle state.
+
+Example 2 represents the hierarchical model of CPUs and domain idle states.
+CPUs define their domain provider in their psci DT node. The domain controls
+the power to the CPU and possibly other h/w blocks that would enter an idle
+state along with the CPU. The CPU's idle states may therefore be considered as
+the domain's idle states and have the compatible "arm,idle-state". Such domains
+may also be embedded within another domain that may represent common h/w blocks
+between these CPUs. The idle states of the CPU topology shall be represented as
+the domain's idle states. Note that for the domain idle state, the
+"arm,psci-suspend-param" represents idle states hierarchically.
+
+In PSCI firmware v1.0, the OS-Initiated mode is introduced. However, the
+flattened vs hierarchical DT representation is orthogonal to the OS-Initiated
+vs the platform-coordinated PSCI CPU suspend modes, thus should be considered
+independent of each other.
+
+The hierarchical representation helps and makes it easy to implement OSI mode
+and OS implementations may choose to mandate it. For the default platform-
+coordinated mode, both representations are viable options.
+
+Example 1: Flattened representation of CPU and domain idle states
+	cpus {
+		#address-cells = <1>;
+		#size-cells = <0>;
+
+		CPU0: cpu@0 {
+			device_type = "cpu";
+			compatible = "arm,cortex-a53", "arm,armv8";
+			reg = <0x0>;
+			enable-method = "psci";
+			cpu-idle-states = <&CPU_PWRDN>, <&CLUSTER_RET>,
+					  <&CLUSTER_PWRDN>;
+		};
+
+		CPU1: cpu@1 {
+			device_type = "cpu";
+			compatible = "arm,cortex-a57", "arm,armv8";
+			reg = <0x100>;
+			enable-method = "psci";
+			cpu-idle-states = <&CPU_PWRDN>, <&CLUSTER_RET>,
+					  <&CLUSTER_PWRDN>;
+		};
+
+		idle-states {
+			CPU_PWRDN: cpu-power-down {
+				compatible = "arm,idle-state";
+				arm,psci-suspend-param = <0x0000001>;
+				entry-latency-us = <10>;
+				exit-latency-us = <10>;
+				min-residency-us = <100>;
+			};
+
+			CLUSTER_RET: cluster-retention {
+				compatible = "arm,idle-state";
+				arm,psci-suspend-param = <0x1000011>;
+				entry-latency-us = <500>;
+				exit-latency-us = <500>;
+				min-residency-us = <2000>;
+			};
+
+			CLUSTER_PWRDN: cluster-power-down {
+				compatible = "arm,idle-state";
+				arm,psci-suspend-param = <0x1000031>;
+				entry-latency-us = <2000>;
+				exit-latency-us = <2000>;
+				min-residency-us = <6000>;
+			};
+	};
+
+	psci {
+		compatible = "arm,psci-0.2";
+		method = "smc";
+	};
+
+Example 2: Hierarchical representation of CPU and domain idle states
+
+	cpus {
+		#address-cells = <1>;
+		#size-cells = <0>;
+
+		CPU0: cpu@0 {
+			device_type = "cpu";
+			compatible = "arm,cortex-a53", "arm,armv8";
+			reg = <0x0>;
+			enable-method = "psci";
+			power-domains = <&CPU_PD0>;
+			power-domain-names = "psci";
+		};
+
+		CPU1: cpu@1 {
+			device_type = "cpu";
+			compatible = "arm,cortex-a57", "arm,armv8";
+			reg = <0x100>;
+			enable-method = "psci";
+			power-domains = <&CPU_PD1>;
+			power-domain-names = "psci";
+		};
+
+		idle-states {
+			CPU_PWRDN: cpu-power-down {
+				compatible = "arm,idle-state";
+				arm,psci-suspend-param = <0x0000001>;
+				entry-latency-us = <10>;
+				exit-latency-us = <10>;
+				min-residency-us = <100>;
+			};
+
+			CLUSTER_RET: cluster-retention {
+				compatible = "domain-idle-state";
+				arm,psci-suspend-param = <0x1000010>;
+				entry-latency-us = <500>;
+				exit-latency-us = <500>;
+				min-residency-us = <2000>;
+			};
+
+			CLUSTER_PWRDN: cluster-power-down {
+				compatible = "domain-idle-state";
+				arm,psci-suspend-param = <0x1000030>;
+				entry-latency-us = <2000>;
+				exit-latency-us = <2000>;
+				min-residency-us = <6000>;
+			};
+		};
+	};
+
+	psci {
+		compatible = "arm,psci-1.0";
+		method = "smc";
+
+		CPU_PD0: cpu-pd0 {
+			#power-domain-cells = <0>;
+			domain-idle-states = <&CPU_PWRDN>;
+			power-domains = <&CLUSTER_PD>;
+		};
+
+		CPU_PD1: cpu-pd1 {
+			#power-domain-cells = <0>;
+			domain-idle-states =  <&CPU_PWRDN>;
+			power-domains = <&CLUSTER_PD>;
+		};
+
+		CLUSTER_PD: cluster-pd {
+			#power-domain-cells = <0>;
+			domain-idle-states = <&CLUSTER_RET>, <&CLUSTER_PWRDN>;
+		};
+	};
+
 [1] Kernel documentation - ARM idle states bindings
     Documentation/devicetree/bindings/arm/idle-states.txt
 [2] Power State Coordination Interface (PSCI) specification
     http://infocenter.arm.com/help/topic/com.arm.doc.den0022c/DEN0022C_Power_State_Coordination_Interface.pdf
+[3]. PM Domains description
+    Documentation/devicetree/bindings/power/power_domain.txt
-- 
2.17.1