"Rafael J. Wysocki" <rjw@xxxxxxx> writes: > On Wednesday, June 22, 2011, Kevin Hilman wrote: >> "Rafael J. Wysocki" <rjw@xxxxxxx> writes: >> >> > From: Rafael J. Wysocki <rjw@xxxxxxx> >> > >> > Make generic PM domains support system-wide power transitions >> > (system suspend and hibernation). Add suspend, resume, freeze, thaw, >> > poweroff and restore callbacks to be associated with struct >> > generic_pm_domain objects and make pm_genpd_init() use them as >> > appropriate. >> > >> > The new callbacks do nothing for devices belonging to power domains >> > that were powered down at run time (before the transition). >> >> Great, this is the approach I prefer too, but... >> >> Now I'm confused. Leaving runtime suspended devices alone is what I was >> doing in my subsystem but was told not to. According to >> >> http://www.mail-archive.com/linux-omap@xxxxxxxxxxxxxxx/msg50690.html >> >> "it's generally agreed that _all_ devices should return to full >> power during system resume -- even if they were runtime suspended >> before the system sleep." > > Well, let's say this part of the documentation is slightly outdated. > > It basically refers to the model in which system suspend is a separate global > hardware or firmware operation, so the state of devices may be changed by the > BIOS or whatever takes over control in the meantime. In that case the kernel > has to ensure that the states of devices are consistent with what it thinks > about them and the simplest way to achieve that is to put the devices to > full power during resume (and back to low power if that's desirable). > > However, in the case of the systems this patchset is intended for system > suspend is achieved by putting various hardware components into low-power > states directly in a coordinated way and the system sleep state effectively > follows from the low-power states the hardware components end up in. The > system is woken up from this state by an interrupt or another mechanism under > the kernel's control. As a result, the kernel never gives control away, so > the state of devices after the resume is precisely known to it. > In consequence, it need not ensure that the state of devices is consistent with > its view, because it knows that this is the case. :-) > > So the documentation should be updated to say what hardware model it is > referring to. Great! Thanks for the clarification. Kevin _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
