diff options
Diffstat (limited to 'Documentation/power/pm_qos_interface.txt')
| -rw-r--r-- | Documentation/power/pm_qos_interface.txt | 104 |
1 files changed, 89 insertions, 15 deletions
diff --git a/Documentation/power/pm_qos_interface.txt b/Documentation/power/pm_qos_interface.txt index 79a2a58425e..a5da5c7e712 100644 --- a/Documentation/power/pm_qos_interface.txt +++ b/Documentation/power/pm_qos_interface.txt @@ -7,7 +7,7 @@ one of the 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. +constraints and PM QoS flags. Each parameters have defined units: * latency: usec @@ -86,15 +86,21 @@ To remove the user mode request for a target value simply close the device node. -2. PM QoS per-device latency framework +2. PM QoS per-device latency and flags 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. +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. Two device PM QoS flags are defined currently: PM_QOS_FLAG_NO_POWER_OFF +and PM_QOS_FLAG_REMOTE_WAKEUP. + +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: @@ -119,6 +125,40 @@ the request. s32 dev_pm_qos_read_value(device): 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 attributes +pm_qos_no_power_off and pm_qos_remote_wakeup under the device's power directory +allowing user space to change these flags' value. + +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 attributes pm_qos_no_power_off and pm_qos_remote_wakeup +under the device's power directory. Notification mechanisms: The per-device PM QoS framework has 2 different and distinct notification trees: @@ -127,7 +167,7 @@ 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. +is changed (for resume latency device PM QoS only). int dev_pm_qos_remove_notifier(device, notifier): Removes the notification callback function for the device. @@ -135,14 +175,48 @@ 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. +The callback is called when the aggregated value for any device is changed +(for resume latency device PM QoS only). 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. - +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. |