Quoting Lorenzo Pieralisi (2014-05-06 11:04:38)
> diff --git a/Documentation/devicetree/bindings/arm/idle-states.txt b/Documentation/devicetree/bindings/arm/idle-states.txt
> new file mode 100644
> index 0000000..196ef52
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/arm/idle-states.txt
> @@ -0,0 +1,508 @@
...
> +===========================================
> +2 - idle-states node
> +===========================================
> +
> +ARM processor idle states are defined within the idle-states node, which is
> +a direct child of the cpus node [1] and provides a container where the
> +processor idle states, defined as device tree nodes, are listed.
> +
> +- idle-states node
> +
> + Usage: Optional - On ARM systems, is a container of processor idle
> + states nodes. If the system does not provide CPU
> + power management capabilities or the processor just
> + supports idle_standby an idle-states node is not
> + required.
> +
> + Description: idle-states node is a container node, where its
> + subnodes describe the CPU idle states.
> +
> + Node name must be "idle-states".
> +
> + The idle-states node's parent node must be the cpus node.
> +
> + The idle-states node's child nodes can be:
> +
> + - one or more state nodes
> +
> + Any other configuration is considered invalid.
> +
> + An idle-states node defines the following properties:
> +
> + - entry-method
> + Usage: Required
> + Value type: <stringlist>
> + Definition: Describes the method by which a CPU enters the
> + idle states. This property is required and must be
> + one of:
> +
> + - "arm,psci"
> + ARM PSCI firmware interface [2].
> +
> + - "[vendor],[method]"
> + An implementation dependent string with
> + format "vendor,method", where vendor is a string
> + denoting the name of the manufacturer and
> + method is a string specifying the mechanism
> + used to enter the idle state.
> +
> +The nodes describing the idle states (state) can only be defined within the
> +idle-states node.
> +
> +Any other configuration is consider invalid and therefore must be ignored.
consider -> considered
must be -> shall?
Is the reference to "any other configuration" referring to state nodes
not in the idle states node? If so, maybe this sentence should go
together with that one.
> +===========================================
> +4 - Examples
> +===========================================
> +
> +Example 1 (ARM 64-bit, 16-cpu system):
> +
> +cpus {
> + #size-cells = <0>;
> + #address-cells = <2>;
> +
> + idle-states {
> + entry-method = "arm,psci";
> +
> + CPU_RETENTION_0_0: cpu-retention-0-0 {
> + compatible = "arm,idle-state";
> + cache-state-retained;
> + entry-method-param = <0x0010000>;
> + entry-latency-us = <20>;
> + exit-latency-us = <40>;
> + min-residency-us = <30>;
> + };
> +
> + CLUSTER_RETENTION_0: cluster-retention-0 {
> + compatible = "arm,idle-state";
> + logic-state-retained;
> + cache-state-retained;
> + entry-method-param = <0x1010000>;
> + entry-latency-us = <50>;
> + exit-latency-us = <100>;
> + min-residency-us = <250>;
> + };
...
> + };
> +
> + CPU0: cpu@0 {
> + device_type = "cpu";
> + compatible = "arm,cortex-a57";
> + reg = <0x0 0x0>;
> + enable-method = "psci";
> + cpu-idle-states = <&CPU_RETENTION_0_0 &CPU_SLEEP_0_0
> + &CLUSTER_RETENTION_0 &CLUSTER_SLEEP_0>;
> + };
> +
> + CPU1: cpu@1 {
> + device_type = "cpu";
> + compatible = "arm,cortex-a57";
> + reg = <0x0 0x1>;
> + enable-method = "psci";
> + cpu-idle-states = <&CPU_RETENTION_0_0 &CPU_SLEEP_0_0
> + &CLUSTER_RETENTION_0 &CLUSTER_SLEEP_0>;
> + };
How can we specify what states are entered together vs. those that
are independent (since they also share the entry-method-param)?
CPU_SLEEP_0_0 is used for both CPU0 and CPU1, yet each cpu can enter
it without waiting for the other. Whereas CLUSTER_RETENTION_0 should
not be entered until all CPUs sharing it enter.
Is the idea to define separate CPU_SLEEP/CPU_RETENTION nodes for each cpu?
Thanks!
Sebastian
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