Re: [RFD] Automatic suspend

Rafael J. Wysocki
2009-02-20T20:56:11Z

On Friday 20 February 2009, Kyle Moffett wrote:
> On Fri, Feb 20, 2009 at 10:56 AM, Rafael J. Wysocki <rjw@sisk.pl> wrote:
> > * Introduce /sys/power/sleep that will work like /sys/power/state, but:
> > - First, it will call ->acknowledge() for each driver (via bus types) to
> > check if any of them wants to postpone the suspend (this will prevent tasks
> > from being frozen unnecessarily if it is known in advance that the suspend
> > should not happen at the moment).
> > - Next, it will check the "I_do_not_want_automatic_suspend_to_occur" flag
> > of each process and the suspend will be aborted if it is true for any of
> > them (quite frankly, I think that should be integrated with the freezer,
> > in particular the tasks that have TIF_FREEZE set shouldn't be able to set
> > this flag and it should be checked in the freezer loop for every task with
> > TIF_FREEZE unset).
> > - Next, it will proceed with suspending just like /sys/power/state does (the
> > drivers that missed the opportunity to abort the suspend by returning
> > 'false' from ->acknowledge() can still abort the suspend by failing their
> > ->suspend() routines).
> >
> > Then, the decision making logic will be able to use /sys/power/sleep whenever
> > it wishes to and the kernel will be able to refuse to suspend if it's not
> > desirable at the moment.
>
> Then, for a userspace process handling input events:
>
> 1) Unset "no-suspend flag"
> 2) Poll event device
> 3) When the poll returns true, set the "no-suspend flag"
> 4) Read the event device and process the event(s)
> 5) Go back to step 1
>
> The event driver would responsible for atomically preventing suspend
> from the moment a button is pressed until it is actually delivered to
> a userspace process. Since at that time the userspace process will be
> preventing suspend, there will be no window in which we could go to
> sleep with pending events.

That's correct.

How would you like to prevent it from happening?

Rafael