1=============================
2Subsystem Trace Points: power
3=============================
4
5The power tracing system captures events related to power transitions
6within the kernel. Broadly speaking there are three major subheadings:
7
8  - Power state switch which reports events related to suspend (S-states),
9    cpuidle (C-states) and cpufreq (P-states)
10  - System clock related changes
11  - Power domains related changes and transitions
12
13This document describes what each of the tracepoints is and why they
14might be useful.
15
16Cf. include/trace/events/power.h for the events definitions.
17
181. Power state switch events
19============================
20
211.1 Trace API
22-----------------
23
24A 'cpu' event class gathers the CPU-related events: cpuidle and
25cpufreq.
26::
27
28  cpu_idle		"state=%lu cpu_id=%lu"
29  cpu_frequency		"state=%lu cpu_id=%lu"
30
31A suspend event is used to indicate the system going in and out of the
32suspend mode:
33::
34
35  machine_suspend		"state=%lu"
36
37
38Note: the value of '-1' or '4294967295' for state means an exit from the current state,
39i.e. trace_cpu_idle(4, smp_processor_id()) means that the system
40enters the idle state 4, while trace_cpu_idle(PWR_EVENT_EXIT, smp_processor_id())
41means that the system exits the previous idle state.
42
43The event which has 'state=4294967295' in the trace is very important to the user
44space tools which are using it to detect the end of the current state, and so to
45correctly draw the states diagrams and to calculate accurate statistics etc.
46
472. Clocks events
48================
49The clock events are used for clock enable/disable and for
50clock rate change.
51::
52
53  clock_enable		"%s state=%lu cpu_id=%lu"
54  clock_disable		"%s state=%lu cpu_id=%lu"
55  clock_set_rate		"%s state=%lu cpu_id=%lu"
56
57The first parameter gives the clock name (e.g. "gpio1_iclk").
58The second parameter is '1' for enable, '0' for disable, the target
59clock rate for set_rate.
60
613. Power domains events
62=======================
63The power domain events are used for power domains transitions
64::
65
66  power_domain_target	"%s state=%lu cpu_id=%lu"
67
68The first parameter gives the power domain name (e.g. "mpu_pwrdm").
69The second parameter is the power domain target state.
70
714. PM QoS events
72================
73The PM QoS events are used for QoS add/update/remove request and for
74target/flags update.
75::
76
77  pm_qos_add_request                 "pm_qos_class=%s value=%d"
78  pm_qos_update_request              "pm_qos_class=%s value=%d"
79  pm_qos_remove_request              "pm_qos_class=%s value=%d"
80  pm_qos_update_request_timeout      "pm_qos_class=%s value=%d, timeout_us=%ld"
81
82The first parameter gives the QoS class name (e.g. "CPU_DMA_LATENCY").
83The second parameter is value to be added/updated/removed.
84The third parameter is timeout value in usec.
85::
86
87  pm_qos_update_target               "action=%s prev_value=%d curr_value=%d"
88  pm_qos_update_flags                "action=%s prev_value=0x%x curr_value=0x%x"
89
90The first parameter gives the QoS action name (e.g. "ADD_REQ").
91The second parameter is the previous QoS value.
92The third parameter is the current QoS value to update.
93
94And, there are also events used for device PM QoS add/update/remove request.
95::
96
97  dev_pm_qos_add_request             "device=%s type=%s new_value=%d"
98  dev_pm_qos_update_request          "device=%s type=%s new_value=%d"
99  dev_pm_qos_remove_request          "device=%s type=%s new_value=%d"
100
101The first parameter gives the device name which tries to add/update/remove
102QoS requests.
103The second parameter gives the request type (e.g. "DEV_PM_QOS_RESUME_LATENCY").
104The third parameter is value to be added/updated/removed.
105