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