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-rw-r--r--Documentation/power/pm_qos_interface.txt48
1 files changed, 25 insertions, 23 deletions
diff --git a/Documentation/power/pm_qos_interface.txt b/Documentation/power/pm_qos_interface.txt
index c40866e8b957..bfed898a03fc 100644
--- a/Documentation/power/pm_qos_interface.txt
+++ b/Documentation/power/pm_qos_interface.txt
@@ -18,44 +18,46 @@ and pm_qos_params.h. This is done because having the available parameters
18being runtime configurable or changeable from a driver was seen as too easy to 18being runtime configurable or changeable from a driver was seen as too easy to
19abuse. 19abuse.
20 20
21For each parameter a list of performance requirements is maintained along with 21For each parameter a list of performance requests is maintained along with
22an aggregated target value. The aggregated target value is updated with 22an aggregated target value. The aggregated target value is updated with
23changes to the requirement list or elements of the list. Typically the 23changes to the request list or elements of the list. Typically the
24aggregated target value is simply the max or min of the requirement values held 24aggregated target value is simply the max or min of the request values held
25in the parameter list elements. 25in the parameter list elements.
26 26
27From kernel mode the use of this interface is simple: 27From kernel mode the use of this interface is simple:
28pm_qos_add_requirement(param_id, name, target_value):
29Will insert a named element in the list for that identified PM_QOS parameter
30with the target value. Upon change to this list the new target is recomputed
31and any registered notifiers are called only if the target value is now
32different.
33 28
34pm_qos_update_requirement(param_id, name, new_target_value): 29handle = pm_qos_add_request(param_class, target_value):
35Will search the list identified by the param_id for the named list element and 30Will insert an element into the list for that identified PM_QOS class with the
36then update its target value, calling the notification tree if the aggregated 31target value. Upon change to this list the new target is recomputed and any
37target is changed. with that name is already registered. 32registered notifiers are called only if the target value is now different.
33Clients of pm_qos need to save the returned handle.
38 34
39pm_qos_remove_requirement(param_id, name): 35void pm_qos_update_request(handle, new_target_value):
40Will search the identified list for the named element and remove it, after 36Will update the list element pointed to by the handle with the new target value
41removal it will update the aggregate target and call the notification tree if 37and recompute the new aggregated target, calling the notification tree if the
42the target was changed as a result of removing the named requirement. 38target is changed.
39
40void pm_qos_remove_request(handle):
41Will remove the element. After removal it will update the aggregate target and
42call the notification tree if the target was changed as a result of removing
43the request.
43 44
44 45
45From user mode: 46From user mode:
46Only processes can register a pm_qos requirement. To provide for automatic 47Only processes can register a pm_qos request. To provide for automatic
47cleanup for process the interface requires the process to register its 48cleanup of a process, the interface requires the process to register its
48parameter requirements in the following way: 49parameter requests in the following way:
49 50
50To register the default pm_qos target for the specific parameter, the process 51To register the default pm_qos target for the specific parameter, the process
51must open one of /dev/[cpu_dma_latency, network_latency, network_throughput] 52must open one of /dev/[cpu_dma_latency, network_latency, network_throughput]
52 53
53As long as the device node is held open that process has a registered 54As long as the device node is held open that process has a registered
54requirement on the parameter. The name of the requirement is "process_<PID>" 55request on the parameter.
55derived from the current->pid from within the open system call.
56 56
57To change the requested target value the process needs to write a s32 value to 57To change the requested target value the process needs to write an s32 value to
58the open device node. This translates to a pm_qos_update_requirement call. 58the open device node. Alternatively the user mode program could write a hex
59string for the value using 10 char long format e.g. "0x12345678". This
60translates to a pm_qos_update_request call.
59 61
60To remove the user mode request for a target value simply close the device 62To remove the user mode request for a target value simply close the device
61node. 63node.