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bf1db69f | 1 | PM Quality Of Service Interface. |
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2 | |
3 | This interface provides a kernel and user mode interface for registering | |
4 | performance expectations by drivers, subsystems and user space applications on | |
5 | one of the parameters. | |
6 | ||
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7 | Two different PM QoS frameworks are available: |
8 | 1. PM QoS classes for cpu_dma_latency, network_latency, network_throughput. | |
9 | 2. the per-device PM QoS framework provides the API to manage the per-device latency | |
10 | constraints. | |
d82b3518 | 11 | |
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12 | Each parameters have defined units: |
13 | * latency: usec | |
14 | * timeout: usec | |
15 | * throughput: kbs (kilo bit / sec) | |
16 | ||
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17 | |
18 | 1. PM QoS framework | |
19 | ||
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20 | The infrastructure exposes multiple misc device nodes one per implemented |
21 | parameter. The set of parameters implement is defined by pm_qos_power_init() | |
22 | and pm_qos_params.h. This is done because having the available parameters | |
23 | being runtime configurable or changeable from a driver was seen as too easy to | |
24 | abuse. | |
25 | ||
ed77134b | 26 | For each parameter a list of performance requests is maintained along with |
d82b3518 | 27 | an aggregated target value. The aggregated target value is updated with |
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28 | changes to the request list or elements of the list. Typically the |
29 | aggregated target value is simply the max or min of the request values held | |
d82b3518 | 30 | in the parameter list elements. |
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31 | Note: the aggregated target value is implemented as an atomic variable so that |
32 | reading the aggregated value does not require any locking mechanism. | |
33 | ||
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34 | |
35 | From kernel mode the use of this interface is simple: | |
d82b3518 | 36 | |
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37 | void pm_qos_add_request(handle, param_class, target_value): |
38 | Will insert an element into the list for that identified PM QoS class with the | |
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39 | target value. Upon change to this list the new target is recomputed and any |
40 | registered notifiers are called only if the target value is now different. | |
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41 | Clients of pm_qos need to save the returned handle for future use in other |
42 | pm_qos API functions. | |
d82b3518 | 43 | |
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44 | void pm_qos_update_request(handle, new_target_value): |
45 | Will update the list element pointed to by the handle with the new target value | |
46 | and recompute the new aggregated target, calling the notification tree if the | |
47 | target is changed. | |
48 | ||
49 | void pm_qos_remove_request(handle): | |
50 | Will remove the element. After removal it will update the aggregate target and | |
51 | call the notification tree if the target was changed as a result of removing | |
52 | the request. | |
d82b3518 | 53 | |
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54 | int pm_qos_request(param_class): |
55 | Returns the aggregated value for a given PM QoS class. | |
56 | ||
57 | int pm_qos_request_active(handle): | |
58 | Returns if the request is still active, i.e. it has not been removed from a | |
59 | PM QoS class constraints list. | |
60 | ||
61 | int pm_qos_add_notifier(param_class, notifier): | |
62 | Adds a notification callback function to the PM QoS class. The callback is | |
63 | called when the aggregated value for the PM QoS class is changed. | |
64 | ||
65 | int pm_qos_remove_notifier(int param_class, notifier): | |
66 | Removes the notification callback function for the PM QoS class. | |
67 | ||
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68 | |
69 | From user mode: | |
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70 | Only processes can register a pm_qos request. To provide for automatic |
71 | cleanup of a process, the interface requires the process to register its | |
72 | parameter requests in the following way: | |
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73 | |
74 | To register the default pm_qos target for the specific parameter, the process | |
75 | must open one of /dev/[cpu_dma_latency, network_latency, network_throughput] | |
76 | ||
77 | As long as the device node is held open that process has a registered | |
ed77134b | 78 | request on the parameter. |
d82b3518 | 79 | |
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80 | To change the requested target value the process needs to write an s32 value to |
81 | the open device node. Alternatively the user mode program could write a hex | |
82 | string for the value using 10 char long format e.g. "0x12345678". This | |
83 | translates to a pm_qos_update_request call. | |
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84 | |
85 | To remove the user mode request for a target value simply close the device | |
86 | node. | |
87 | ||
88 | ||
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89 | 2. PM QoS per-device latency framework |
90 | ||
91 | For each device a list of performance requests is maintained along with | |
92 | an aggregated target value. The aggregated target value is updated with | |
93 | changes to the request list or elements of the list. Typically the | |
94 | aggregated target value is simply the max or min of the request values held | |
95 | in the parameter list elements. | |
96 | Note: the aggregated target value is implemented as an atomic variable so that | |
97 | reading the aggregated value does not require any locking mechanism. | |
98 | ||
99 | ||
100 | From kernel mode the use of this interface is the following: | |
101 | ||
ae0fb4b7 | 102 | int dev_pm_qos_add_request(device, handle, type, value): |
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103 | Will insert an element into the list for that identified device with the |
104 | target value. Upon change to this list the new target is recomputed and any | |
105 | registered notifiers are called only if the target value is now different. | |
106 | Clients of dev_pm_qos need to save the handle for future use in other | |
107 | dev_pm_qos API functions. | |
108 | ||
109 | int dev_pm_qos_update_request(handle, new_value): | |
110 | Will update the list element pointed to by the handle with the new target value | |
111 | and recompute the new aggregated target, calling the notification trees if the | |
112 | target is changed. | |
113 | ||
114 | int dev_pm_qos_remove_request(handle): | |
115 | Will remove the element. After removal it will update the aggregate target and | |
116 | call the notification trees if the target was changed as a result of removing | |
117 | the request. | |
118 | ||
119 | s32 dev_pm_qos_read_value(device): | |
120 | Returns the aggregated value for a given device's constraints list. | |
121 | ||
122 | ||
123 | Notification mechanisms: | |
124 | The per-device PM QoS framework has 2 different and distinct notification trees: | |
125 | a per-device notification tree and a global notification tree. | |
126 | ||
127 | int dev_pm_qos_add_notifier(device, notifier): | |
128 | Adds a notification callback function for the device. | |
129 | The callback is called when the aggregated value of the device constraints list | |
130 | is changed. | |
131 | ||
132 | int dev_pm_qos_remove_notifier(device, notifier): | |
133 | Removes the notification callback function for the device. | |
134 | ||
135 | int dev_pm_qos_add_global_notifier(notifier): | |
136 | Adds a notification callback function in the global notification tree of the | |
137 | framework. | |
138 | The callback is called when the aggregated value for any device is changed. | |
139 | ||
140 | int dev_pm_qos_remove_global_notifier(notifier): | |
141 | Removes the notification callback function from the global notification tree | |
142 | of the framework. | |
143 | ||
144 | ||
145 | From user mode: | |
146 | No API for user space access to the per-device latency constraints is provided | |
147 | yet - still under discussion. | |
d82b3518 | 148 |