--- /dev/null
- s32 dev_pm_qos_read_value(device):
+===============================
+PM Quality Of Service Interface
+===============================
+
+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.
+
+Two different PM QoS frameworks are available:
+1. PM QoS classes for cpu_dma_latency, network_latency, network_throughput,
+memory_bandwidth.
+2. the per-device PM QoS framework provides the API to manage the per-device latency
+constraints and PM QoS flags.
+
+Each parameters have defined units:
+
+ * latency: usec
+ * timeout: usec
+ * throughput: kbs (kilo bit / sec)
+ * memory bandwidth: mbs (mega 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
+being runtime configurable or changeable from a driver was seen as too easy to
+abuse.
+
+For each parameter 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 simple:
+
+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 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
+ and recompute the new aggregated target, calling the notification tree if the
+ target is changed.
+
+void pm_qos_remove_request(handle):
+ 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
+cleanup of a process, the interface requires the process to register its
+parameter requests in the following way:
+
+To register the default pm_qos target for the specific parameter, the process
+must open one of /dev/[cpu_dma_latency, network_latency, network_throughput]
+
+As long as the device node is held open that process has a registered
+request on the parameter.
+
+To change the requested target value the process needs to write an s32 value to
+the open device node. Alternatively the user mode program could write a hex
+string for the value using 10 char long format e.g. "0x12345678". This
+translates to a pm_qos_update_request call.
+
+To remove the user mode request for a target value simply close the device
+node.
+
+
+2. PM QoS per-device latency and flags framework
+================================================
+
+For each device, there are three lists of PM QoS requests. Two of them are
+maintained along with the aggregated targets of resume latency and active
+state latency tolerance (in microseconds) and the third one is for PM QoS flags.
+Values are updated in response to changes of the request list.
+
+The target values of resume latency and active state latency tolerance are
+simply the minimum of the request values held in the parameter list elements.
+The PM QoS flags aggregate value is a gather (bitwise OR) of all list elements'
+values. One device PM QoS flag is defined currently: PM_QOS_FLAG_NO_POWER_OFF.
+
+Note: The aggregated target values are implemented in such a way 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, type, 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.
+
- int dev_pm_qos_add_notifier(device, notifier):
- Adds a notification callback function for the device.
++s32 dev_pm_qos_read_value(device, type):
+ Returns the aggregated value for a given device's constraints list.
+
+enum pm_qos_flags_status dev_pm_qos_flags(device, mask)
+ Check PM QoS flags of the given device against the given mask of flags.
+ The meaning of the return values is as follows:
+
+ PM_QOS_FLAGS_ALL:
+ All flags from the mask are set
+ PM_QOS_FLAGS_SOME:
+ Some flags from the mask are set
+ PM_QOS_FLAGS_NONE:
+ No flags from the mask are set
+ PM_QOS_FLAGS_UNDEFINED:
+ The device's PM QoS structure has not been initialized
+ or the list of requests is empty.
+
+int dev_pm_qos_add_ancestor_request(dev, handle, type, value)
+ Add a PM QoS request for the first direct ancestor of the given device whose
+ power.ignore_children flag is unset (for DEV_PM_QOS_RESUME_LATENCY requests)
+ or whose power.set_latency_tolerance callback pointer is not NULL (for
+ DEV_PM_QOS_LATENCY_TOLERANCE requests).
+
+int dev_pm_qos_expose_latency_limit(device, value)
+ Add a request to the device's PM QoS list of resume latency constraints and
+ create a sysfs attribute pm_qos_resume_latency_us under the device's power
+ directory allowing user space to manipulate that request.
+
+void dev_pm_qos_hide_latency_limit(device)
+ Drop the request added by dev_pm_qos_expose_latency_limit() from the device's
+ PM QoS list of resume latency constraints and remove sysfs attribute
+ pm_qos_resume_latency_us from the device's power directory.
+
+int dev_pm_qos_expose_flags(device, value)
+ Add a request to the device's PM QoS list of flags and create sysfs attribute
+ pm_qos_no_power_off under the device's power directory allowing user space to
+ change the value of the PM_QOS_FLAG_NO_POWER_OFF flag.
+
+void dev_pm_qos_hide_flags(device)
+ Drop the request added by dev_pm_qos_expose_flags() from the device's PM QoS list
+ of flags and remove sysfs attribute pm_qos_no_power_off from the device's power
+ directory.
+
+Notification mechanisms:
+
+The per-device PM QoS framework has a per-device notification tree.
+
- is changed (for resume latency device PM QoS only).
++int dev_pm_qos_add_notifier(device, notifier, type):
++ Adds a notification callback function for the device for a particular request
++ type.
++
+ The callback is called when the aggregated value of the device constraints list
- int dev_pm_qos_remove_notifier(device, notifier):
++ is changed.
+
++int dev_pm_qos_remove_notifier(device, notifier, type):
+ Removes the notification callback function for the device.
+
+
+Active state latency tolerance
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+This device PM QoS type is used to support systems in which hardware may switch
+to energy-saving operation modes on the fly. In those systems, if the operation
+mode chosen by the hardware attempts to save energy in an overly aggressive way,
+it may cause excess latencies to be visible to software, causing it to miss
+certain protocol requirements or target frame or sample rates etc.
+
+If there is a latency tolerance control mechanism for a given device available
+to software, the .set_latency_tolerance callback in that device's dev_pm_info
+structure should be populated. The routine pointed to by it is should implement
+whatever is necessary to transfer the effective requirement value to the
+hardware.
+
+Whenever the effective latency tolerance changes for the device, its
+.set_latency_tolerance() callback will be executed and the effective value will
+be passed to it. If that value is negative, which means that the list of
+latency tolerance requirements for the device is empty, the callback is expected
+to switch the underlying hardware latency tolerance control mechanism to an
+autonomous mode if available. If that value is PM_QOS_LATENCY_ANY, in turn, and
+the hardware supports a special "no requirement" setting, the callback is
+expected to use it. That allows software to prevent the hardware from
+automatically updating the device's latency tolerance in response to its power
+state changes (e.g. during transitions from D3cold to D0), which generally may
+be done in the autonomous latency tolerance control mode.
+
+If .set_latency_tolerance() is present for the device, sysfs attribute
+pm_qos_latency_tolerance_us will be present in the devivce's power directory.
+Then, user space can use that attribute to specify its latency tolerance
+requirement for the device, if any. Writing "any" to it means "no requirement,
+but do not let the hardware control latency tolerance" and writing "auto" to it
+allows the hardware to be switched to the autonomous mode if there are no other
+requirements from the kernel side in the device's list.
+
+Kernel code can use the functions described above along with the
+DEV_PM_QOS_LATENCY_TOLERANCE device PM QoS type to add, remove and update
+latency tolerance requirements for devices.
projects / platform / kernel / linux-rpi.git / commitdiff