arm/msm/qcom%2Cidle-state.txt

3 ARM provides idle-state node to define the cpuidle states, as defined in [1].
4 cpuidle-qcom is the cpuidle driver for Qualcomm SoCs and uses these idle
6 The idle states supported by the QCOM SoC are defined as -
14 When the WFI instruction is executed the ARM core would gate its internal
17 interrupt to trigger the core back in to active. This triggers the cache
20 cache hierarchy is also out of standby, and then the cpu is allowed to resume
26 Retention: Retention is a low power state where the core is clock gated and
27 the memory and the registers associated with the core are retained. The
30 sequence and would wait for interrupt, before restoring the cpu to execution
33 Standalone PC: A cpu can power down and warmboot if there is a sufficient time
35 to indicate a core entering a power down state without consulting any other
36 cpu or the system resources. This helps save power only on that core.  The SPM
38 core, wait for the interrupt, restore power to the core, and ensure the
39 system state including cache hierarchy is ready before allowing core to
40 resume. Applying power and resetting the core causes the core to warmboot
42 kernel. Entering a power down state for the cpu, needs to be done by trapping
44 code in the EL for the SoC. On SoCs with write-back L1 cache, the cache has to
45 be flushed in s/w, before powering down the core.
48 itself in that the cpu acknowledges and permits the SoC to enter deeper sleep
50 be flushed, system bus, clocks - lowered, and SoC main XO clock gated and
53 of this low power mode would be considered high even though at a cpu level,
54 this essentially is cpu power down. The SPM in this state also may handshake
58 The idle-state for QCOM SoCs are distinguished by the compatible property of
59 the idle-states device node.
61 The devicetree representation of the idle state should be -
65 - compatible: Must be one of -
66 			"qcom,idle-state-ret",
67 			"qcom,idle-state-spc",
68 			"qcom,idle-state-pc",
69 		and "arm,idle-state".
75 	idle-states {
77 			compatible = "qcom,idle-state-spc", "arm,idle-state";
78 			entry-latency-us = <150>;
79 			exit-latency-us = <200>;
80 			min-residency-us = <2000>;
84 [1]. Documentation/devicetree/bindings/arm/idle-states.yaml