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-rw-r--r--Documentation/power/pm_qos_interface.txt92
1 files changed, 5 insertions, 87 deletions
diff --git a/Documentation/power/pm_qos_interface.txt b/Documentation/power/pm_qos_interface.txt
index 79a2a58425e..bfed898a03f 100644
--- a/Documentation/power/pm_qos_interface.txt
+++ b/Documentation/power/pm_qos_interface.txt
@@ -4,19 +4,14 @@ This interface provides a kernel and user mode interface for registering
4performance expectations by drivers, subsystems and user space applications on 4performance expectations by drivers, subsystems and user space applications on
5one of the parameters. 5one of the parameters.
6 6
7Two different PM QoS frameworks are available: 7Currently we have {cpu_dma_latency, network_latency, network_throughput} as the
81. PM QoS classes for cpu_dma_latency, network_latency, network_throughput. 8initial set of pm_qos parameters.
92. the per-device PM QoS framework provides the API to manage the per-device latency
10constraints.
11 9
12Each parameters have defined units: 10Each parameters have defined units:
13 * latency: usec 11 * latency: usec
14 * timeout: usec 12 * timeout: usec
15 * throughput: kbs (kilo bit / sec) 13 * throughput: kbs (kilo bit / sec)
16 14
17
181. PM QoS framework
19
20The infrastructure exposes multiple misc device nodes one per implemented 15The infrastructure exposes multiple misc device nodes one per implemented
21parameter. The set of parameters implement is defined by pm_qos_power_init() 16parameter. The set of parameters implement is defined by pm_qos_power_init()
22and pm_qos_params.h. This is done because having the available parameters 17and pm_qos_params.h. This is done because having the available parameters
@@ -28,18 +23,14 @@ an aggregated target value. The aggregated target value is updated with
28changes to the request list or elements of the list. Typically the 23changes to the request list or elements of the list. Typically the
29aggregated target value is simply the max or min of the request values held 24aggregated target value is simply the max or min of the request values held
30in the parameter list elements. 25in the parameter list elements.
31Note: the aggregated target value is implemented as an atomic variable so that
32reading the aggregated value does not require any locking mechanism.
33
34 26
35From kernel mode the use of this interface is simple: 27From kernel mode the use of this interface is simple:
36 28
37void pm_qos_add_request(handle, param_class, target_value): 29handle = pm_qos_add_request(param_class, target_value):
38Will insert an element into the list for that identified PM QoS class with the 30Will insert an element into the list for that identified PM_QOS class with the
39target value. Upon change to this list the new target is recomputed and any 31target value. Upon change to this list the new target is recomputed and any
40registered notifiers are called only if the target value is now different. 32registered notifiers are called only if the target value is now different.
41Clients of pm_qos need to save the returned handle for future use in other 33Clients of pm_qos need to save the returned handle.
42pm_qos API functions.
43 34
44void pm_qos_update_request(handle, new_target_value): 35void pm_qos_update_request(handle, new_target_value):
45Will update the list element pointed to by the handle with the new target value 36Will update the list element pointed to by the handle with the new target value
@@ -51,20 +42,6 @@ Will remove the element. After removal it will update the aggregate target and
51call the notification tree if the target was changed as a result of removing 42call the notification tree if the target was changed as a result of removing
52the request. 43the request.
53 44
54int pm_qos_request(param_class):
55Returns the aggregated value for a given PM QoS class.
56
57int pm_qos_request_active(handle):
58Returns if the request is still active, i.e. it has not been removed from a
59PM QoS class constraints list.
60
61int pm_qos_add_notifier(param_class, notifier):
62Adds a notification callback function to the PM QoS class. The callback is
63called when the aggregated value for the PM QoS class is changed.
64
65int pm_qos_remove_notifier(int param_class, notifier):
66Removes the notification callback function for the PM QoS class.
67
68 45
69From user mode: 46From user mode:
70Only processes can register a pm_qos request. To provide for automatic 47Only processes can register a pm_qos request. To provide for automatic
@@ -86,63 +63,4 @@ To remove the user mode request for a target value simply close the device
86node. 63node.
87 64
88 65
892. PM QoS per-device latency framework
90
91For each device a list of performance requests is maintained along with
92an aggregated target value. The aggregated target value is updated with
93changes to the request list or elements of the list. Typically the
94aggregated target value is simply the max or min of the request values held
95in the parameter list elements.
96Note: the aggregated target value is implemented as an atomic variable so that
97reading the aggregated value does not require any locking mechanism.
98
99
100From kernel mode the use of this interface is the following:
101
102int dev_pm_qos_add_request(device, handle, type, value):
103Will insert an element into the list for that identified device with the
104target value. Upon change to this list the new target is recomputed and any
105registered notifiers are called only if the target value is now different.
106Clients of dev_pm_qos need to save the handle for future use in other
107dev_pm_qos API functions.
108
109int dev_pm_qos_update_request(handle, new_value):
110Will update the list element pointed to by the handle with the new target value
111and recompute the new aggregated target, calling the notification trees if the
112target is changed.
113
114int dev_pm_qos_remove_request(handle):
115Will remove the element. After removal it will update the aggregate target and
116call the notification trees if the target was changed as a result of removing
117the request.
118
119s32 dev_pm_qos_read_value(device):
120Returns the aggregated value for a given device's constraints list.
121
122
123Notification mechanisms:
124The per-device PM QoS framework has 2 different and distinct notification trees:
125a per-device notification tree and a global notification tree.
126
127int dev_pm_qos_add_notifier(device, notifier):
128Adds a notification callback function for the device.
129The callback is called when the aggregated value of the device constraints list
130is changed.
131
132int dev_pm_qos_remove_notifier(device, notifier):
133Removes the notification callback function for the device.
134
135int dev_pm_qos_add_global_notifier(notifier):
136Adds a notification callback function in the global notification tree of the
137framework.
138The callback is called when the aggregated value for any device is changed.
139
140int dev_pm_qos_remove_global_notifier(notifier):
141Removes the notification callback function from the global notification tree
142of the framework.
143
144
145From user mode:
146No API for user space access to the per-device latency constraints is provided
147yet - still under discussion.
148 66