PM / QoS: Update Documentation for the pm_qos and dev_pm_qos frameworks

Update the documentation for the recently updated pm_qos API, kernel
and user space.  Add documentation for the per-device PM QoS
(dev_pm_qos) framework API.

Signed-off-by: Jean Pihet <j-pihet@ti.com>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>

Documentation/power/pm_qos_interface.txt

@@ -4,14 +4,19 @@ This interface provides a kernel and user mode interface for registering
 performance expectations by drivers, subsystems and user space applications on
 one of the parameters.
 
-Currently we have {cpu_dma_latency, network_latency, network_throughput} as the
-initial set of pm_qos parameters.
+Two different PM QoS frameworks are available:
+1. PM QoS classes for cpu_dma_latency, network_latency, network_throughput.
+2. the per-device PM QoS framework provides the API to manage the per-device latency
+constraints.
 
 Each parameters have defined units:
  * latency: usec
  * timeout: usec
  * throughput: kbs (kilo bit / sec)
 
+
+1. PM QoS framework
+
 The infrastructure exposes multiple misc device nodes one per implemented
 parameter.  The set of parameters implement is defined by pm_qos_power_init()
 and pm_qos_params.h.  This is done because having the available parameters
@@ -23,14 +28,18 @@ an aggregated target value.  The aggregated target value is updated with
 changes to the request list or elements of the list.  Typically the
 aggregated target value is simply the max or min of the request values held
 in the parameter list elements.
+Note: the aggregated target value is implemented as an atomic variable so that
+reading the aggregated value does not require any locking mechanism.
+
 
 From kernel mode the use of this interface is simple:
 
-handle = pm_qos_add_request(param_class, target_value):
-Will insert an element into the list for that identified PM_QOS class with the
+void pm_qos_add_request(handle, param_class, target_value):
+Will insert an element into the list for that identified PM QoS class with the
 target value.  Upon change to this list the new target is recomputed and any
 registered notifiers are called only if the target value is now different.
-Clients of pm_qos need to save the returned handle.
+Clients of pm_qos need to save the returned handle for future use in other
+pm_qos API functions.
 
 void pm_qos_update_request(handle, new_target_value):
 Will update the list element pointed to by the handle with the new target value
@@ -42,6 +51,20 @@ Will remove the element.  After removal it will update the aggregate target and
 call the notification tree if the target was changed as a result of removing
 the request.
 
+int pm_qos_request(param_class):
+Returns the aggregated value for a given PM QoS class.
+
+int pm_qos_request_active(handle):
+Returns if the request is still active, i.e. it has not been removed from a
+PM QoS class constraints list.
+
+int pm_qos_add_notifier(param_class, notifier):
+Adds a notification callback function to the PM QoS class. The callback is
+called when the aggregated value for the PM QoS class is changed.
+
+int pm_qos_remove_notifier(int param_class, notifier):
+Removes the notification callback function for the PM QoS class.
+
 
 From user mode:
 Only processes can register a pm_qos request.  To provide for automatic
@@ -63,4 +86,63 @@ To remove the user mode request for a target value simply close the device
 node.
 
 
+2. PM QoS per-device latency framework
+
+For each device a list of performance requests is maintained along with
+an aggregated target value.  The aggregated target value is updated with
+changes to the request list or elements of the list.  Typically the
+aggregated target value is simply the max or min of the request values held
+in the parameter list elements.
+Note: the aggregated target value is implemented as an atomic variable so that
+reading the aggregated value does not require any locking mechanism.
+
+
+From kernel mode the use of this interface is the following:
+
+int dev_pm_qos_add_request(device, handle, value):
+Will insert an element into the list for that identified device with the
+target value.  Upon change to this list the new target is recomputed and any
+registered notifiers are called only if the target value is now different.
+Clients of dev_pm_qos need to save the handle for future use in other
+dev_pm_qos API functions.
+
+int dev_pm_qos_update_request(handle, new_value):
+Will update the list element pointed to by the handle with the new target value
+and recompute the new aggregated target, calling the notification trees if the
+target is changed.
+
+int dev_pm_qos_remove_request(handle):
+Will remove the element.  After removal it will update the aggregate target and
+call the notification trees if the target was changed as a result of removing
+the request.
+
+s32 dev_pm_qos_read_value(device):
+Returns the aggregated value for a given device's constraints list.
+
+
+Notification mechanisms:
+The per-device PM QoS framework has 2 different and distinct notification trees:
+a per-device notification tree and a global notification tree.
+
+int dev_pm_qos_add_notifier(device, notifier):
+Adds a notification callback function for the device.
+The callback is called when the aggregated value of the device constraints list
+is changed.
+
+int dev_pm_qos_remove_notifier(device, notifier):
+Removes the notification callback function for the device.
+
+int dev_pm_qos_add_global_notifier(notifier):
+Adds a notification callback function in the global notification tree of the
+framework.
+The callback is called when the aggregated value for any device is changed.
+
+int dev_pm_qos_remove_global_notifier(notifier):
+Removes the notification callback function from the global notification tree
+of the framework.
+
+
+From user mode:
+No API for user space access to the per-device latency constraints is provided
+yet - still under discussion.