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| -rw-r--r-- | Documentation/power/runtime_pm.txt | 50 |
1 files changed, 50 insertions, 0 deletions
diff --git a/Documentation/power/runtime_pm.txt b/Documentation/power/runtime_pm.txt index 7b5ab270124..356fd86f4ea 100644 --- a/Documentation/power/runtime_pm.txt +++ b/Documentation/power/runtime_pm.txt @@ -381,3 +381,53 @@ incremented by the core before executing ->probe() and ->remove(). Still, it 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. + +6. Run-time PM and System Sleep + +Run-time PM and system sleep (i.e., system suspend and hibernation, also known +as suspend-to-RAM and suspend-to-disk) interact with each other in a couple of +ways. If a device is active when a system sleep starts, everything is +straightforward. But what should happen if the device is already suspended? + +The device may have different wake-up settings for run-time PM and system sleep. +For example, remote wake-up may be enabled for run-time suspend but disallowed +for system sleep (device_may_wakeup(dev) returns 'false'). When this happens, +the subsystem-level system suspend callback is responsible for changing the +device's wake-up setting (it may leave that to the device driver's system +suspend routine). It may be necessary to resume the device and suspend it again +in order to do so. The same is true if the driver uses different power levels +or other settings for run-time suspend and system sleep. + +During system resume, devices generally should be brought back to full power, +even if they were suspended before the system sleep began. There are several +reasons for this, including: + + * The device might need to switch power levels, wake-up settings, etc. + + * Remote wake-up events might have been lost by the firmware. + + * The device's children may need the device to be at full power in order + to resume themselves. + + * The driver's idea of the device state may not agree with the device's + physical state. This can happen during resume from hibernation. + + * The device might need to be reset. + + * Even though the device was suspended, if its usage counter was > 0 then most + likely it would need a run-time resume in the near future anyway. + + * Always going back to full power is simplest. + +If the device was suspended before the sleep began, then its run-time PM status +will have to be updated to reflect the actual post-system sleep status. The way +to do this is: + + pm_runtime_disable(dev); + pm_runtime_set_active(dev); + pm_runtime_enable(dev); + +The PM core always increments the run-time usage counter before calling the +->prepare() callback and decrements it after calling the ->complete() callback. +Hence disabling run-time PM temporarily like this will not cause any run-time +suspend callbacks to be lost. |