On 一, 2012-02-13 at 10:01 -0500, Alan Stern wrote: > On Mon, 13 Feb 2012, Lin Ming wrote: > > > From: Zhang Rui <rui.zhang@xxxxxxxxx> > > > > 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. > Exactly. what I'm trying to fix here is to add a "special" runtime low power state, aka, power off. > 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? > I thought about this before, e.g. introduce support for multiple runtime low power states in runtime PM core, like suspend/hibernate for system low power states. But I'm not sure if this is workable because the low power states varies between devices/buses/platforms. So I decided to introduce a special low power state, aka, runtime power off, first, which means the same thing to different devices/buses/platforms. thanks, rui -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
