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SubjectRe: [RFD] Automatic suspend
On Fri, Feb 20, 2009 at 10:56 AM, Rafael J. Wysocki <> 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.

Kyle Moffett

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