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Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/power/devices.txt | 49 |
1 files changed, 0 insertions, 49 deletions
diff --git a/Documentation/power/devices.txt b/Documentation/power/devices.txt index d0e79d5820a5..c53d26361919 100644 --- a/Documentation/power/devices.txt +++ b/Documentation/power/devices.txt @@ -502,52 +502,3 @@ If the CPU can have a "cpufreq" driver, there also may be opportunities to shift to lower voltage settings and reduce the power cost of executing a given number of instructions. (Without voltage adjustment, it's rare for cpufreq to save much power; the cost-per-instruction must go down.) - - -/sys/devices/.../power/state files -================================== -For now you can also test some of this functionality using sysfs. - - DEPRECATED: USE "power/state" ONLY FOR DRIVER TESTING, AND - AVOID USING dev->power.power_state IN DRIVERS. - - THESE WILL BE REMOVED. IF THE "power/state" FILE GETS REPLACED, - IT WILL BECOME SOMETHING COUPLED TO THE BUS OR DRIVER. - -In each device's directory, there is a 'power' directory, which contains -at least a 'state' file. The value of this field is effectively boolean, -PM_EVENT_ON or PM_EVENT_SUSPEND. - - * Reading from this file displays a value corresponding to - the power.power_state.event field. All nonzero values are - displayed as "2", corresponding to a low power state; zero - is displayed as "0", corresponding to normal operation. - - * Writing to this file initiates a transition using the - specified event code number; only '0', '2', and '3' are - accepted (without a newline); '2' and '3' are both - mapped to PM_EVENT_SUSPEND. - -On writes, the PM core relies on that recorded event code and the device/bus -capabilities to determine whether it uses a partial suspend() or resume() -sequence to change things so that the recorded event corresponds to the -numeric parameter. - - - If the bus requires the irqs-disabled suspend_late()/resume_early() - phases, writes fail because those operations are not supported here. - - - If the recorded value is the expected value, nothing is done. - - - If the recorded value is nonzero, the device is partially resumed, - using the bus.resume() and/or class.resume() methods. - - - If the target value is nonzero, the device is partially suspended, - using the class.suspend() and/or bus.suspend() methods and the - PM_EVENT_SUSPEND message. - -Drivers have no way to tell whether their suspend() and resume() calls -have come through the sysfs power/state file or as part of entering a -system sleep state, except that when accessed through sysfs the normal -parent/child sequencing rules are ignored. Drivers (such as bus, bridge, -or hub drivers) which expose child devices may need to enforce those rules -on their own. |
