On Friday, 21 September 2007 20:11, Jeremy Maitin-Shepard wrote: > "Rafael J. Wysocki" <rjw@xxxxxxx> writes: > > > On Friday, 21 September 2007 15:14, huang ying wrote: > >> On 9/21/07, Rafael J. Wysocki <rjw@xxxxxxx> wrote: > >> > On Friday, 21 September 2007 05:33, Eric W. Biederman wrote: > >> > > Nigel Cunningham <nigel@xxxxxxxxxxxxxxxxxx> writes: > > [--snip--] > >> > > > >> > > No one has yet attacked the hard problem of coming up with separate > >> > > hibernate methods for drivers. > >> > > >> > Well, I've been playing a bit with that for some time, but it's not easy by > > any > >> > means. > >> > > >> > In short, I'm seeing some problems related to the handling of ACPI that seem > > to > >> > shatter the entire idea of having separate hibernate methods, at least as > > far > >> > as ACPI systems are concerned. > >> > >> So sadly to hear this. Can you details it a little? Or a link? > > > Well, the problem is that apparently some systems (eg. my HP nx6325) expect us > > to execute the _PTS ACPI global control method before creating the image _and_ > > to execute acpi_enter_sleep_state(ACPI_STATE_S4) in order to finally put the > > system into the sleep state. In particular, on nx6325, if we don't do that, > > then after the restore the status of the AC power will not be reported > > correctly (and if you replace the battery while in the sleep state, the > > battery status will not be updated correctly after the restore). Similar > > issues have been reported for other machines. > > Suppose that instead of using ACPI S4 state at all, you instead just > power off. Yes, you'll lose wakeup event functionality, and flashy > LEDs, but doesn't this take care of the problem? Nope. > The firmware shouldn't see the hibernate as anything other than a shutdown > and reboot. Actually, this assumption is apparently wrong. > ACPI should be initialized normally when resuming, which should take care of > getting AC power status reported properly. Well, that doesn't work. I've tested it, really. :-) > This should be the behavior, anyway, on the many systems that do not > support S4. > > > Now, the ACPI specification requires us to put devices into low power states > > before executing _PTS and that's exactly what we're doing before a suspend to > > RAM. Thus, it seems that in general we need to do the same for hibernation on > > ACPI systems. > > It seems that if ACPI S4 is going to be used, Switching to low power > state is something that should be done only immediately before entering > that state (i.e. after the image has already been saved). Doesn't. Work. > In particular, it should not be done just before the atomic copy. It is > true that (during resume) after the atomic copy snapshot is restored, > drivers will need to be prepared (i.e. have saved whatever information > is necessary) to _resume_ devices from the low power state, but that > does not mean they have to actually be put into that low power state > before the copy is made. > > I agree that for the kexec implementation there may be additional > issues. For swsusp, uswsusp, and tuxonice, though, I don't see why > there should be a problem. I think that, as was recognized before, all > of the issues are resolved by properly considering exactly what each > callback should do and when it should be called. The problems stem from > ambiguous specifications, or trying to use the same callback for two > different purposes or in two different cases. > > Let me know if I'm mistaken. See above. :-) Greetings, Rafael _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
