Fix synchronizing issue of Kobo front light between KOReader and nickel (#2977)

frontend/device/generic/powerd.lua

@@ -35,6 +35,7 @@ function BasePowerD:setIntensityHW(intensity) end
 function BasePowerD:getCapacityHW() return 0 end
 function BasePowerD:isChargingHW() return false end
 function BasePowerD:frontlightIntensityHW() return 0 end
+function BasePowerD:isFrontlightOnHW() return self.fl_intensity > self.fl_min end
 function BasePowerD:turnOffFrontlightHW() self:_setIntensity(self.fl_min) end
 function BasePowerD:turnOnFrontlightHW() self:_setIntensity(self.fl_intensity) end
 -- Anything needs to be done before do a real hardware suspend. Such as turn off
@@ -52,7 +53,7 @@ end
 function BasePowerD:_decideFrontlightState()
     assert(self ~= nil)
     assert(self.device.hasFrontlight())
-    self.is_fl_on = (self.fl_intensity > self.fl_min)
+    self.is_fl_on = self:isFrontlightOnHW()
 end
 
 function BasePowerD:isFrontlightOff()

frontend/device/kobo/powerd.lua

@@ -32,7 +32,7 @@ end
 function KoboPowerD:_syncNickelConf()
     if self.has_fl_state_cfg and KOBO_SYNC_BRIGHTNESS_WITH_NICKEL then
         NickelConf.frontLightState.set(self:isFrontlightOn())
-        NickelConf.frontLightLevel.set(self:frontlightIntensity())
+        NickelConf.frontLightLevel.set(self.fl_intensity)
     end
 end
 
@@ -43,6 +43,13 @@ function KoboPowerD:frontlightIntensityHW()
     return 20
 end
 
+function KoboPowerD:isFrontlightOnHW()
+    if self.has_fl_state_cfg then
+        return NickelConf.frontLightState.get()
+    end
+    return BasePowerD.isFrontlightOnHW(self)
+end
+
 function KoboPowerD:turnOffFrontlightHW() self:_setIntensity(0) end
 
 function KoboPowerD:setIntensityHW(intensity)