Kobo: Fix a few bad interactions between suspend & checkUnexpectedWakeup (#9499)

* Kobo: Make sure checkUnexpectedWakeup won't run between scheduled
suspend calls

Because of the suspend_wait_timeout, a previously scheduled check *could* shortcircuit a suspend scheduled a tiny bit later by a real Power event.
This led to fun breakage when you plugged/unplugged a "sleeping" device, for instance.

Fix #9457

* And clear up the unexpected_wakeup_count semantics

Bits of an older design seeped through and were causing weird corner-cases...

frontend/device/generic/device.lua

@@ -284,7 +284,7 @@ function Device:onPowerEvent(ev)
             -- Already in screen saver mode, no need to update UI/state before
             -- suspending the hardware. This usually happens when sleep cover
             -- is closed after the device was sent to suspend state.
-            logger.dbg("Already in screen saver mode, suspending...")
+            logger.dbg("Already in screen saver mode, going back to suspend...")
             self:rescheduleSuspend()
         end
     -- else we were not in screensaver mode

frontend/device/kobo/device.lua

@@ -847,6 +847,14 @@ local function getProductId()
     return product_id
 end
 
+-- NOTE: We overload this to make sure checkUnexpectedWakeup doesn't trip *before* the newly scheduled suspend
+function Kobo:rescheduleSuspend()
+    local UIManager = require("ui/uimanager")
+    UIManager:unschedule(self.suspend)
+    UIManager:unschedule(self.checkUnexpectedWakeup)
+    UIManager:scheduleIn(self.suspend_wait_timeout, self.suspend, self)
+end
+
 function Kobo:checkUnexpectedWakeup()
     local UIManager = require("ui/uimanager")
     -- Just in case another event like SleepCoverClosed also scheduled a suspend
@@ -864,10 +872,8 @@ function Kobo:checkUnexpectedWakeup()
     else
         -- We've hit an early resume, assume this is unexpected (as we only run if Kobo:resume hasn't already).
         logger.dbg("Kobo suspend: checking unexpected wakeup number", self.unexpected_wakeup_count)
-        if self.unexpected_wakeup_count == 0 or self.unexpected_wakeup_count > 20 then
-            -- Don't put device back to sleep under the following two cases:
-            --   1. a resume event triggered Kobo:resume() function
-            --   2. trying to put device back to sleep more than 20 times after unexpected wakeup
+        if self.unexpected_wakeup_count > 20 then
+            -- If we've failed to put the device back to sleep over 20 consecutive times, we give up.
             -- Broadcast a specific event, so that AutoSuspend can pick up the baton...
             local Event = require("ui/event")
             UIManager:broadcastEvent(Event:new("UnexpectedWakeupLimit"))
@@ -879,8 +885,6 @@ function Kobo:checkUnexpectedWakeup()
     end
 end
 
-function Kobo:getUnexpectedWakeup() return self.unexpected_wakeup_count end
-
 --- The function to put the device into standby, with enabled touchscreen.
 -- max_duration ... maximum time for the next standby, can wake earlier (e.g. Tap, Button ...)
 function Kobo:standby(max_duration)
@@ -1034,10 +1038,8 @@ function Kobo:suspend()
     -- NOTE: We unflag /sys/power/state-extended in Kobo:resume() to keep
     --       things tidy and easier to follow
 
-    -- Kobo:resume() will reset unexpected_wakeup_count = 0 to signal an
-    -- expected wakeup, which gets checked in checkUnexpectedWakeup().
+    -- Kobo:resume() will reset unexpected_wakeup_count and unschedule the check to signal a sane wakeup.
     self.unexpected_wakeup_count = self.unexpected_wakeup_count + 1
-    -- We're assuming Kobo:resume() will be called in the next 15 seconds in ordrer to cancel that check.
     logger.dbg("Kobo suspend: scheduling unexpected wakeup guard")
     UIManager:scheduleIn(15, self.checkUnexpectedWakeup, self)
 end
@@ -1080,8 +1082,11 @@ function Kobo:resume()
 end
 
 function Kobo:usbPlugOut()
-    -- Reset the unexpected wakeup shenanigans, since we're no longer charging, meaning power savings are now critical again ;).
-    self.unexpected_wakeup_count = 0
+    -- Rewind the unexpected wakeup counter, since we're no longer charging, meaning power savings are now critical again ;).
+    -- NOTE: We don't reset it to 0 because, semantically, only resume should ever be allowed to do so.
+    if self.unexpected_wakeup_count > 0 then
+        self.unexpected_wakeup_count = 1
+    end
 end
 
 function Kobo:saveSettings()