On Friday, 27 April 2007 16:34, Alan Stern wrote: > On Fri, 27 Apr 2007, Johannes Berg wrote: > > > Look at it now: > > > > * FREEZE Quiesce operations so that a consistent image can be saved; > > * but do NOT otherwise enter a low power device state, and do > > * NOT emit system wakeup events. > > * > > * PRETHAW Quiesce as if for FREEZE; additionally, prepare for restoring > > * the system from a snapshot taken after an earlier FREEZE. > > * Some drivers will need to reset their hardware state instead > > * of preserving it, to ensure that it's never mistaken for the > > * state which that earlier snapshot had set up. > > > > Why is prethaw even necessary? As far as I can tell it's only necessary > > because resume() can't tell you whether you just want to thaw or need to > > reset since it doesn't tell you at what point it's invoked. > > I think you're wrong here. It's a little hard to say because the > terminology is confusing and not yet standardized. > > For the sake of argument, let's call the stages of STD and STR by these > names (also noted are the current PSMG values): > > Suspend to disk: > "prepare to create snapshot" (= FREEZE) > "continue after snapshot" (= RESUME) > > Resume from disk: > "prepare to restore snapshot" (= PRETHAW) > "continue after restore" (= RESUME) > > Suspend to RAM: > "suspend" (= SUSPEND) > "resume" (= RESUME) > > The real reason for adding PRETHAW was that drivers couldn't distinguish > between "continue after restore" and "resume", other than by examining the > device's state -- since the PM core doesn't pass any information to the > resume() method. > > I suppose we could have modified the "prepare to create snapshot" code > instead, but doing so would mean that "continue after snapshot" and > "continue after restore" would always do the same thing, which is not > necessarily a good idea. > > Anyway, based on this analysis it seems reasonable to have Six (6) method > pointers. Suggested names (in the same order as above): > > pre_snaphot() > post_snapshot() > pre_restore() > post_restore() > suspend() > resume() > > People apparently assume that pre_snapshot() and pre_restore() would > always do the same thing and hence be redundant. I'm not so sure; time > will tell. Doing it this way certainly is more clear. How do we differentiate between post_snapshot() and post_restore()? I mean, after the restore we're entering the same code path as after the snapshot, so do we use a global var for this purpose? Rafael _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
