On Tuesday, 17 July 2007 22:24, Jeremy Maitin-Shepard wrote: > "Rafael J. Wysocki" <rjw@xxxxxxx> writes: > > [snip] > > > Well, first, the fact is that _some_ systems _will_ be powered while in > > hibernation (the majority of notebooks, for example) and you should assume > > that the platform _may_ retain some information accross the hibernation/restore > > cycle. In that case you _should_ _not_ trash the information retained by the > > platform. > > I'm not sure the majority of notebook users will want wakeup support in > exchange for some power consumption while the system is off. I think > many people would not consider the trouble of having to press the power > button instead of merely opening the lid too great. > > Furthermore, S4 mode is of course also not suitable if you intend to > replace the battery while the system is hibernated. > > It does seem that it is useful to provide S4 as an option, but certainly > just shutting down should also be an option on all systems. > > > Now, with that in mind, ACPI requires us to make the system enter the S4 sleep > > state as a result of the hibernation procedure. In my opinion this may be done > > after saving the image, but still this means, for example, that the > > image-saving kernel needs to support ACPI. > > It seems that it most certainly must be done AFTER saving the image, as > the image obviously cannot be saved after entering S4 state, since S4 > state is nearly the same as powering off completely and all memory will > be lost. > > > Next, during the restore, we should first check if the image is present (and > > valid) _without_ turning ACPI on (note that this is not done by the current > > hibernation code and that leads to strange problems on some systems). Then, > > if the image is present (and valid), we should first load it, jump to the > > hibernated kernel and _then_ turn ACPI on and execute the _BFS and > > _WAK ACPI global methods (again, this is not done by the current code in that > > order, which is wrong). Only after that is the hibernated kernel supposed to > > continue. > > It seems that the implementation of that behavior for Linux cannot be > quite so simple, since resume from hibernation is driven (in general) > from an initrd/initramfs rather than directly from the kernel > initialization sequence, in order to support modular drivers and > features like DM and LVM. That's correct. > Thus, there would have to be a new "delay_acpi_initialization" kernel > command-line option. Additionally, there would be a sysfs interface to > tell the kernel to proceed with the ACPI initialization as normal. This > would be used by an initrd/initramfs after determining that a resume > from hibernate will not be done. If a resume from hibernate is done, > this hook won't be used, and instead the resumed kernel will call the > ACPI hibernate resume stuff if S4 state was used; otherwise, the resumed > kernel will just re-initialize ACPI as normal. Also, if the in-kernel > code for checking if a resume can be done does not find a hibernate > image, it will also invoke the delayed ACPI initialization. Yes, something like this. My point is, though, that it really requires some thought and needs to be remebered about. Greetings, Rafael -- "Premature optimization is the root of all evil." - Donald Knuth _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
