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| -rw-r--r-- | Documentation/power/runtime_pm.txt | 28 |
1 files changed, 28 insertions, 0 deletions
diff --git a/Documentation/power/runtime_pm.txt b/Documentation/power/runtime_pm.txt index 356fd86f4ea..f1937064168 100644 --- a/Documentation/power/runtime_pm.txt +++ b/Documentation/power/runtime_pm.txt @@ -224,6 +224,12 @@ defined in include/linux/pm.h: RPM_SUSPENDED, which means that each device is initially regarded by the PM core as 'suspended', regardless of its real hardware status + unsigned int runtime_auto; + - if set, indicates that the user space has allowed the device driver to + power manage the device at run time via the /sys/devices/.../power/control + interface; it may only be modified with the help of the pm_runtime_allow() + and pm_runtime_forbid() helper functions + All of the above fields are members of the 'power' member of 'struct device'. 4. Run-time PM Device Helper Functions @@ -329,6 +335,16 @@ drivers/base/power/runtime.c and include/linux/pm_runtime.h: 'power.runtime_error' is set or 'power.disable_depth' is greater than zero) + void pm_runtime_allow(struct device *dev); + - set the power.runtime_auto flag for the device and decrease its usage + counter (used by the /sys/devices/.../power/control interface to + effectively allow the device to be power managed at run time) + + void pm_runtime_forbid(struct device *dev); + - unset the power.runtime_auto flag for the device and increase its usage + counter (used by the /sys/devices/.../power/control interface to + effectively prevent the device from being power managed at run time) + It is safe to execute the following helper functions from interrupt context: pm_request_idle() @@ -382,6 +398,18 @@ may be desirable to suspend the device as soon as ->probe() or ->remove() has finished, so the PM core uses pm_runtime_idle_sync() to invoke the subsystem-level idle callback for the device at that time. +The user space can effectively disallow the driver of the device to power manage +it at run time by changing the value of its /sys/devices/.../power/control +attribute to "on", which causes pm_runtime_forbid() to be called. In principle, +this mechanism may also be used by the driver to effectively turn off the +run-time power management of the device until the user space turns it on. +Namely, during the initialization the driver can make sure that the run-time PM +status of the device is 'active' and call pm_runtime_forbid(). It should be +noted, however, that if the user space has already intentionally changed the +value of /sys/devices/.../power/control to "auto" to allow the driver to power +manage the device at run time, the driver may confuse it by using +pm_runtime_forbid() this way. + 6. Run-time PM and System Sleep Run-time PM and system sleep (i.e., system suspend and hibernation, also known |