[RFC PATCH v1] PM: wakeup: Provide interface for userspace to abort suspend

[Saravana Kannan <saravanak@google.com>]

Once suspend starts, it can take a while before file system sync
finishes and all the userspace threads are frozen. During this time,
there can be events that originate in userspace that would require the
suspend to be aborted.

The only way to abort suspend from userspace as of today is to grab
and release a kernel wakelock using the /sys/power/wake_lock and
/sys/power/wake_unlock files. This has the disadvantage of:

* Doing the useless work of creating and destroying wakelocks.
* If the userspace entity crashes after the wake lock is created, we
  get a wake lock/memory leak.

To avoid all this and simplify the interface, this patch allows
canceling a suspend by writing UINT_MAX value to the
/sys/power/wakeup_count that is meant for tracking wakeup events.

Signed-off-by: Saravana Kannan <saravanak@google.com>
---

Rafael,

If the idea looks good to you, I can also update Documentation and sent
it as a non-RFC patch. I'm not too tied on what file we use to trigger
an abort from userspace as long as it's possible.

Thanks,
Saravana

 drivers/base/power/wakeup.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/base/power/wakeup.c b/drivers/base/power/wakeup.c
index d1283ff1080b..9316de561bcc 100644
--- a/drivers/base/power/wakeup.c
+++ b/drivers/base/power/wakeup.c
@@ -1008,6 +1008,8 @@ bool pm_save_wakeup_count(unsigned int count)
 	if (cnt == count && inpr == 0) {
 		saved_count = count;
 		events_check_enabled = true;
+	} else if (cnt == UINT_MAX) {
+		pm_system_wakeup();
 	}
 	raw_spin_unlock_irqrestore(&events_lock, flags);
 	return events_check_enabled;
-- 
2.50.0.727.gbf7dc18ff4-goog