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Commit d30b82a4 authored by lan,Tianyu's avatar lan,Tianyu Committed by Rafael J. Wysocki
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PM / QoS: Update Documentation/power/pm_qos_interface.txt 



Update PM QoS documentation after recent changes.

[rjw: Changelog]
Signed-off-by: default avatarLan Tianyu <tianyu.lan@intel.com>
Signed-off-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
parent bb177fed

Documentation/power/pm_qos_interface.txt

+43 −7
Original line number Diff line number Diff line
@@ -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
@@ -86,13 +86,17 @@ 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, there are two lists of PM QoS requests. One is maintained

along with the aggregated target of latency value and the other is for PM QoS

flags. Values are updated in response to changes of the request list.



Target latency value is 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.



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.
@@ -119,6 +123,38 @@ 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, value)

Add a PM QoS request for the first direct ancestor of the given device whose

power.ignore_children flag is unset.



int dev_pm_qos_expose_latency_limit(device, value)

Add a request to the device's PM QoS list of 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 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: