diff options
Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/ABI/testing/sysfs-devices-power | 27 | ||||
| -rw-r--r-- | Documentation/power/pm_qos_interface.txt | 82 | ||||
| -rw-r--r-- | Documentation/trace/events-power.txt | 2 |
3 files changed, 87 insertions, 24 deletions
diff --git a/Documentation/ABI/testing/sysfs-devices-power b/Documentation/ABI/testing/sysfs-devices-power index efe449bdf811..7dbf96b724ed 100644 --- a/Documentation/ABI/testing/sysfs-devices-power +++ b/Documentation/ABI/testing/sysfs-devices-power @@ -187,7 +187,7 @@ Description: Not all drivers support this attribute. If it isn't supported, attempts to read or write it will yield I/O errors. -What: /sys/devices/.../power/pm_qos_latency_us +What: /sys/devices/.../power/pm_qos_resume_latency_us Date: March 2012 Contact: Rafael J. Wysocki <rjw@rjwysocki.net> Description: @@ -205,6 +205,31 @@ Description: This attribute has no effect on system-wide suspend/resume and hibernation. +What: /sys/devices/.../power/pm_qos_latency_tolerance_us +Date: January 2014 +Contact: Rafael J. Wysocki <rjw@rjwysocki.net> +Description: + The /sys/devices/.../power/pm_qos_latency_tolerance_us attribute + contains the PM QoS active state latency tolerance limit for the + given device in microseconds. That is the maximum memory access + latency the device can suffer without any visible adverse + effects on user space functionality. If that value is the + string "any", the latency does not matter to user space at all, + but hardware should not be allowed to set the latency tolerance + for the device automatically. + + Reading "auto" from this file means that the maximum memory + access latency for the device may be determined automatically + by the hardware as needed. Writing "auto" to it allows the + hardware to be switched to this mode if there are no other + latency tolerance requirements from the kernel side. + + This attribute is only present if the feature controlled by it + is supported by the hardware. + + This attribute has no effect on runtime suspend and resume of + devices and on system-wide suspend/resume and hibernation. + What: /sys/devices/.../power/pm_qos_no_power_off Date: September 2012 Contact: Rafael J. Wysocki <rjw@rjwysocki.net> diff --git a/Documentation/power/pm_qos_interface.txt b/Documentation/power/pm_qos_interface.txt index 483632087788..a5da5c7e7128 100644 --- a/Documentation/power/pm_qos_interface.txt +++ b/Documentation/power/pm_qos_interface.txt @@ -88,17 +88,19 @@ node. 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. +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. -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. +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 value is implemented as an atomic variable so that -reading the aggregated value does not require any locking mechanism. +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: @@ -132,19 +134,21 @@ The meaning of the return values is as follows: 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) +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. +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 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. +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 latency constraints and remove sysfs attribute pm_qos_resume_latency_us -from the device's power directory. +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 @@ -163,7 +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. @@ -171,14 +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. diff --git a/Documentation/trace/events-power.txt b/Documentation/trace/events-power.txt index 3bd33b8dc7c4..21d514ced212 100644 --- a/Documentation/trace/events-power.txt +++ b/Documentation/trace/events-power.txt @@ -92,5 +92,5 @@ dev_pm_qos_remove_request "device=%s type=%s new_value=%d" The first parameter gives the device name which tries to add/update/remove QoS requests. -The second parameter gives the request type (e.g. "DEV_PM_QOS_LATENCY"). +The second parameter gives the request type (e.g. "DEV_PM_QOS_RESUME_LATENCY"). The third parameter is value to be added/updated/removed. |