1PM Quality Of Service Interface. 2 3This interface provides a kernel and user mode interface for registering 4performance expectations by drivers, subsystems and user space applications on 5one of the parameters. 6 7Currently we have {cpu_dma_latency, network_latency, network_throughput} as the 8initial set of pm_qos parameters. 9 10Each parameters have defined units: 11 * latency: usec 12 * timeout: usec 13 * throughput: kbs (kilo bit / sec) 14 15The infrastructure exposes multiple misc device nodes one per implemented 16parameter. The set of parameters implement is defined by pm_qos_power_init() 17and 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 19abuse. 20 21For each parameter a list of performance requests is maintained along with 22an aggregated target value. The aggregated target value is updated with 23changes to the request list or elements of the list. Typically the 24aggregated target value is simply the max or min of the request values held 25in the parameter list elements. 26 27From kernel mode the use of this interface is simple: 28 29handle = pm_qos_add_request(param_class, target_value): 30Will insert an element into the list for that identified PM_QOS class with the 31target value. Upon change to this list the new target is recomputed and any 32registered notifiers are called only if the target value is now different. 33Clients of pm_qos need to save the returned handle. 34 35void pm_qos_update_request(handle, new_target_value): 36Will update the list element pointed to by the handle with the new target value 37and recompute the new aggregated target, calling the notification tree if the 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. 44 45 46From user mode: 47Only processes can register a pm_qos request. To provide for automatic 48cleanup of a process, the interface requires the process to register its 49parameter requests in the following way: 50 51To register the default pm_qos target for the specific parameter, the process 52must open one of /dev/[cpu_dma_latency, network_latency, network_throughput] 53 54As long as the device node is held open that process has a registered 55request on the parameter. 56 57To change the requested target value the process needs to write an s32 value to 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. 61 62To remove the user mode request for a target value simply close the device 63node. 64 65 66 67