Messages in this thread | | | Date | Mon, 13 Feb 2012 10:01:54 -0500 (EST) | From | Alan Stern <> | Subject | Re: [RFC PATCH 4/6] PM / Runtime: Introduce flag can_power_off |
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On Mon, 13 Feb 2012, Lin Ming wrote:
> From: Zhang Rui <rui.zhang@intel.com> > > Introduce flag can_power_off in device structure to support runtime > power off/on. > > Note that, for a specific device driver, > "support runtime power off/on" means that the driver .runtime_suspend > callback needs to > 1) save all the context so that it can restore the device back to the previous > working state after powered on. > 2) set can_power_off flag to tell the driver model that it's ready for power off. > > The following example shows how this works. > > device A > |---------| > v v > device B device C > > A is the parent of device B and device C, and device A/B/C shares the > same power logic > (Only device A knows how to turn on/off the power). > > In order to power off A, B, C at runtime, > 1) device B and device C should support runtime power off > (runtime suspended with can_power_off flag set) > 2) pm idle request for device A is fired by runtime PM core. > 3) in device A .runtime_suspend callback, it tries to set can_power_off flag. > 4) if succeed, it means all its children have been ready for power off > and it can turn off the power at any time. > 5) if failed, it means at least one of its children does not support runtime > power off, thus the power can not be turned off.
I'm not sure if this is really the right approach. What you're trying to do is implement two different low-power states, basically D3hot and D3cold. Currently the runtime PM core doesn't support such things; all it knows about is low power and full power.
Before doing an ad-hoc implementation, it would be best to step back and think about other subsystems. Other sorts of devices may well have multiple low-power states. What's the best way for this to be supported by the PM core?
Alan Stern
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