On Tuesday, February 14, 2012, Zhang Rui wrote: > Hi, Alan, > > On 一, 2012-02-13 at 15:41 -0500, Alan Stern wrote: > > On Mon, 13 Feb 2012, Rafael J. Wysocki wrote: > > > > > > 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, okay. We can say that this patch tries to implement two different > > "suspended" states, basically "low power" and "power off" (or D3hot and > > D3cold). > > > Right! > > > > > 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). > > > > That's the point. If this is to be implemented outside of the runtime > > PM core, should the patch be allowed to add new fields to struct > > dev_pm_info (which has to be shared among all subsystems)? > > > Surely it shouldn't in this case. > > > Or to put it another way, if we do add new fields to struct dev_pm_info > > (like can_power_off) in order to help support multiple "suspended" > > states, shouldn't these new fields be such that they can be used by > > many different subsystems rather than being special for the > > full-power/no-power situation? > > > My opinion is that the concept of "no-power state" is unique for all > devices/buses/platforms. No, it is not, basically because of power domains. If they are used, then individual device power states are not well defined at all. > If any of them support this, they can use the routines without any > confusion. No, they can't. Thanks, Rafael -- 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
