[RFC PATCH v2 7/8] dt-bindings: Add bindings documentation for RISC-V idle states

[Anup Patel <anup.patel@wdc.com>]

The RISC-V CPU idle states will be described in DT under the
/cpus/idle-states DT node. This patch adds the bindings documentation
for riscv-idle-states DT nodes and idle state DT nodes under it.

Signed-off-by: Anup Patel <anup.patel@wdc.com>
---
 .../devicetree/bindings/riscv/cpus.yaml       |   6 +
 .../bindings/riscv/idle-states.yaml           | 256 ++++++++++++++++++
 2 files changed, 262 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/riscv/idle-states.yaml

diff --git a/Documentation/devicetree/bindings/riscv/cpus.yaml b/Documentation/devicetree/bindings/riscv/cpus.yaml
index e534f6a7cfa1..482936630525 100644
--- a/Documentation/devicetree/bindings/riscv/cpus.yaml
+++ b/Documentation/devicetree/bindings/riscv/cpus.yaml
@@ -95,6 +95,12 @@ properties:
       - compatible
       - interrupt-controller
 
+  cpu-idle-states:
+    $ref: '/schemas/types.yaml#/definitions/phandle-array'
+    description: |
+      List of phandles to idle state nodes supported
+      by this hart (see ./idle-states.yaml).
+
 required:
   - riscv,isa
   - interrupt-controller
diff --git a/Documentation/devicetree/bindings/riscv/idle-states.yaml b/Documentation/devicetree/bindings/riscv/idle-states.yaml
new file mode 100644
index 000000000000..1dbf98905c8e
--- /dev/null
+++ b/Documentation/devicetree/bindings/riscv/idle-states.yaml
@@ -0,0 +1,256 @@
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/riscv/idle-states.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: RISC-V idle states binding description
+
+maintainers:
+  - Anup Patel <anup.patel@wdc.com>
+
+description: |+
+  RISC-V systems can manage power consumption dynamically, where HARTs
+  (or CPUs) [1] can be put in different platform specific suspend (or
+  idle) states (ranging from simple WFI, power gating, etc). The RISC-V
+  SBI [2] hart state management extension provides a standard mechanism
+  for OSes to request HART state transitions.
+
+  The platform specific suspend (or idle) states of a hart can be either
+  retentive or non-rententive in nature. A retentive suspend state will
+  preserve hart register and CSR values for all privilege modes whereas
+  a non-retentive suspend state will not preserve hart register and CSR
+  values. The suspend (or idle) state entered by executing the WFI
+  instruction is considered standard on all RISC-V systems and therefore
+  must not be listed in device tree.
+
+  The device tree binding definition for RISC-V idle states described
+  in this document is quite similar to the ARM idle states [3].
+
+  References
+
+  [1] RISC-V Linux Kernel documentation - CPUs bindings
+      Documentation/devicetree/bindings/riscv/cpus.yaml
+
+  [2] RISC-V Supervisor Binary Interface (SBI)
+      http://github.com/riscv/riscv-sbi-doc/riscv-sbi.adoc
+
+  [3] ARM idle states binding description - Idle states bindings
+      Documentation/devicetree/bindings/arm/idle-states.yaml
+
+properties:
+  $nodename:
+    const: idle-states
+
+patternProperties:
+  "^(cpu|cluster)-":
+    type: object
+    description: |
+      Each state node represents an idle state description and must be
+      defined as follows.
+
+    properties:
+      compatible:
+        const: riscv,idle-state
+
+      riscv,sbi-suspend-param:
+        $ref: /schemas/types.yaml#/definitions/uint32
+        description: |
+          suspend_type parameter to pass to the SBI HSM suspend call. For
+          more details on this parameter SBI specifiation v0.3 (or higher).
+
+      local-timer-stop:
+        description:
+          If present the CPU local timer control logic is lost on state
+          entry, otherwise it is retained.
+        type: boolean
+
+      entry-latency-us:
+        description:
+          Worst case latency in microseconds required to enter the idle state.
+
+      exit-latency-us:
+        description:
+          Worst case latency in microseconds required to exit the idle state.
+          The exit-latency-us duration may be guaranteed only after
+          entry-latency-us has passed.
+
+      min-residency-us:
+        description:
+          Minimum residency duration in microseconds, inclusive of preparation
+          and entry, for this idle state to be considered worthwhile energy
+          wise (refer to section 2 of this document for a complete description).
+
+      wakeup-latency-us:
+        description: |
+          Maximum delay between the signaling of a wake-up event and the CPU
+          being able to execute normal code again. If omitted, this is assumed
+          to be equal to:
+
+            entry-latency-us + exit-latency-us
+
+          It is important to supply this value on systems where the duration
+          of PREP phase (see diagram 1, section 2) is non-neglibigle. In such
+          systems entry-latency-us + exit-latency-us will exceed
+          wakeup-latency-us by this duration.
+
+      idle-state-name:
+        $ref: /schemas/types.yaml#/definitions/string
+        description:
+          A string used as a descriptive name for the idle state.
+
+    required:
+      - compatible
+      - entry-latency-us
+      - exit-latency-us
+      - min-residency-us
+
+additionalProperties: false
+
+examples:
+  - |
+
+    cpus {
+        #size-cells = <0>;
+        #address-cells = <1>;
+
+        cpu@0 {
+            device_type = "cpu";
+            compatible = "riscv";
+            reg = <0x0>;
+            riscv,isa = "rv64imafdc";
+            mmu-type = "riscv,sv48";
+            cpu-idle-states = <&CPU_RET_0_0 &CPU_NONRET_0_0
+                            &CLUSTER_RET_0 &CLUSTER_NONRET_0>;
+
+            cpu_intc0: interrupt-controller {
+                #interrupt-cells = <1>;
+                compatible = "riscv,cpu-intc";
+                interrupt-controller;
+            };
+        };
+
+        cpu@1 {
+            device_type = "cpu";
+            compatible = "riscv";
+            reg = <0x1>;
+            riscv,isa = "rv64imafdc";
+            mmu-type = "riscv,sv48";
+            cpu-idle-states = <&CPU_RET_0_0 &CPU_NONRET_0_0
+                            &CLUSTER_RET_0 &CLUSTER_NONRET_0>;
+
+            cpu_intc1: interrupt-controller {
+                #interrupt-cells = <1>;
+                compatible = "riscv,cpu-intc";
+                interrupt-controller;
+            };
+        };
+
+        cpu@10 {
+            device_type = "cpu";
+            compatible = "riscv";
+            reg = <0x10>;
+            riscv,isa = "rv64imafdc";
+            mmu-type = "riscv,sv48";
+            cpu-idle-states = <&CPU_RET_1_0 &CPU_NONRET_1_0
+                            &CLUSTER_RET_1 &CLUSTER_NONRET_1>;
+
+            cpu_intc10: interrupt-controller {
+                #interrupt-cells = <1>;
+                compatible = "riscv,cpu-intc";
+                interrupt-controller;
+            };
+        };
+
+        cpu@11 {
+            device_type = "cpu";
+            compatible = "riscv";
+            reg = <0x11>;
+            riscv,isa = "rv64imafdc";
+            mmu-type = "riscv,sv48";
+            cpu-idle-states = <&CPU_RET_1_0 &CPU_NONRET_1_0
+                            &CLUSTER_RET_1 &CLUSTER_NONRET_1>;
+
+            cpu_intc11: interrupt-controller {
+                #interrupt-cells = <1>;
+                compatible = "riscv,cpu-intc";
+                interrupt-controller;
+            };
+        };
+
+        idle-states {
+            CPU_RET_0_0: cpu-retentive-0-0 {
+                compatible = "riscv,idle-state";
+                riscv,sbi-suspend-param = <0x10000000>;
+                entry-latency-us = <20>;
+                exit-latency-us = <40>;
+                min-residency-us = <80>;
+            };
+
+            CPU_NONRET_0_0: cpu-nonretentive-0-0 {
+                compatible = "riscv,idle-state";
+                riscv,sbi-suspend-param = <0x90000000>;
+                entry-latency-us = <250>;
+                exit-latency-us = <500>;
+                min-residency-us = <950>;
+            };
+
+            CLUSTER_RET_0: cluster-retentive-0 {
+                compatible = "riscv,idle-state";
+                riscv,sbi-suspend-param = <0x11000000>;
+                local-timer-stop;
+                entry-latency-us = <50>;
+                exit-latency-us = <100>;
+                min-residency-us = <250>;
+                wakeup-latency-us = <130>;
+            };
+
+            CLUSTER_NONRET_0: cluster-nonretentive-0 {
+                compatible = "riscv,idle-state";
+                riscv,sbi-suspend-param = <0x91000000>;
+                local-timer-stop;
+                entry-latency-us = <600>;
+                exit-latency-us = <1100>;
+                min-residency-us = <2700>;
+                wakeup-latency-us = <1500>;
+            };
+
+            CPU_RET_1_0: cpu-retentive-1-0 {
+                compatible = "riscv,idle-state";
+                riscv,sbi-suspend-param = <0x10000010>;
+                entry-latency-us = <20>;
+                exit-latency-us = <40>;
+                min-residency-us = <80>;
+            };
+
+            CPU_NONRET_1_0: cpu-nonretentive-1-0 {
+                compatible = "riscv,idle-state";
+                riscv,sbi-suspend-param = <0x90000010>;
+                entry-latency-us = <250>;
+                exit-latency-us = <500>;
+                min-residency-us = <950>;
+            };
+
+            CLUSTER_RET_1: cluster-retentive-1 {
+                compatible = "riscv,idle-state";
+                riscv,sbi-suspend-param = <0x11000010>;
+                local-timer-stop;
+                entry-latency-us = <50>;
+                exit-latency-us = <100>;
+                min-residency-us = <250>;
+                wakeup-latency-us = <130>;
+            };
+
+            CLUSTER_NONRET_1: cluster-nonretentive-1 {
+                compatible = "riscv,idle-state";
+                riscv,sbi-suspend-param = <0x91000010>;
+                local-timer-stop;
+                entry-latency-us = <600>;
+                exit-latency-us = <1100>;
+                min-residency-us = <2700>;
+                wakeup-latency-us = <1500>;
+            };
+        };
+    };
+
+...
-- 
2.25.1