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  cpu_frequency_limits	"min=%lu max=%lu cpu_id=%lu"
31
32A suspend event is used to indicate the system going in and out of the
33suspend mode:
34::
35
36  machine_suspend		"state=%lu"
37
38
39Note: the value of '-1' or '4294967295' for state means an exit from the current state,
40i.e. trace_cpu_idle(4, smp_processor_id()) means that the system
41enters the idle state 4, while trace_cpu_idle(PWR_EVENT_EXIT, smp_processor_id())
42means that the system exits the previous idle state.
43
44The event which has 'state=4294967295' in the trace is very important to the user
45space tools which are using it to detect the end of the current state, and so to
46correctly draw the states diagrams and to calculate accurate statistics etc.
47
482. Clocks events
49================
50The clock events are used for clock enable/disable and for
51clock rate change.
52::
53
54  clock_enable		"%s state=%lu cpu_id=%lu"
55  clock_disable		"%s state=%lu cpu_id=%lu"
56  clock_set_rate		"%s state=%lu cpu_id=%lu"
57
58The first parameter gives the clock name (e.g. "gpio1_iclk").
59The second parameter is '1' for enable, '0' for disable, the target
60clock rate for set_rate.
61
623. Power domains events
63=======================
64The power domain events are used for power domains transitions
65::
66
67  power_domain_target	"%s state=%lu cpu_id=%lu"
68
69The first parameter gives the power domain name (e.g. "mpu_pwrdm").
70The second parameter is the power domain target state.
71
724. PM QoS events
73================
74The PM QoS events are used for QoS add/update/remove request and for
75target/flags update.
76::
77
78  pm_qos_add_request                 "pm_qos_class=%s value=%d"
79  pm_qos_update_request              "pm_qos_class=%s value=%d"
80  pm_qos_remove_request              "pm_qos_class=%s value=%d"
81  pm_qos_update_request_timeout      "pm_qos_class=%s value=%d, timeout_us=%ld"
82
83The first parameter gives the QoS class name (e.g. "CPU_DMA_LATENCY").
84The second parameter is value to be added/updated/removed.
85The third parameter is timeout value in usec.
86::
87
88  pm_qos_update_target               "action=%s prev_value=%d curr_value=%d"
89  pm_qos_update_flags                "action=%s prev_value=0x%x curr_value=0x%x"
90
91The first parameter gives the QoS action name (e.g. "ADD_REQ").
92The second parameter is the previous QoS value.
93The third parameter is the current QoS value to update.
94
95And, there are also events used for device PM QoS add/update/remove request.
96::
97
98  dev_pm_qos_add_request             "device=%s type=%s new_value=%d"
99  dev_pm_qos_update_request          "device=%s type=%s new_value=%d"
100  dev_pm_qos_remove_request          "device=%s type=%s new_value=%d"
101
102The first parameter gives the device name which tries to add/update/remove
103QoS requests.
104The second parameter gives the request type (e.g. "DEV_PM_QOS_RESUME_LATENCY").
105The third parameter is value to be added/updated/removed.
106