On 一, 2012-02-13 at 20:38 +0100, Rafael J. Wysocki wrote: > On Monday, February 13, 2012, 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. > > I'd rather say all it knows about is "suspended" and "active", which mean > "the device is not processing I/O" and "the device may be processing I/O", > respectively. A "suspended" device may or may not be in a low-power state, > but the runtime PM core doesn't care about that. > yes, I know that. > > 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? > > Well, I honestly don't think there's any way they all can be covered at the > same time and that's why we chose to support only "suspended" and "active" > as defined above. > The handling of multiple low-power states must be > implemented outside of the runtime PM core (like in the PCI core, for example). Surely I'd prefer to implement it in the bus code, :), but the problem is that several buses maybe involved at the same time. Let's take ZPODD for example, ZPODD is attached to a SATA port. Only SATA port knows that it can be runtime powered off, because its ACPI node has _PR3._OFF. But when ATA layer code tries to put SATA port to D3_COLD at runtime,it must make sure all the devices/drivers in the same power domain are ready for power off, and in this case, we need to get this info from SCSI layer. 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
