Backlight off should not transition to dim or off states

backlight_controller.cc

 // Copyright (c) 2011 The Chromium OS Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "power_manager/backlight_controller.h"
 
 #include <gdk/gdkx.h>
 #include <math.h>
 #include <X11/extensions/dpms.h>
 
@@ skipping 110 matching lines @@
         SetPowerState(BACKLIGHT_ACTIVE_OFF);
       // Allow large swing in brightness_offset for absolute brightness
       // outside of clamped brightness region.
       int64 absolute_brightness = als_brightness_level_ + *brightness_offset_;
       *brightness_offset_ += new_brightness - absolute_brightness;
       WriteBrightness();
     }
   }
 }
 
-
 bool BacklightController::SetPowerState(PowerState state) {
   if (state == state_ || !is_initialized_)
     return false;
   CHECK(state != BACKLIGHT_UNINITIALIZED);
 
+  // If backlight is turned off, do not transition to dim or off states.
+  // From ACTIVE_OFF state only transition to ACTIVE_ON and SUSPEND states.
+  if (state_ == BACKLIGHT_ACTIVE_OFF && (state == BACKLIGHT_IDLE_OFF ||
+                                         state == BACKLIGHT_DIM))
+    return false;
+
   LOG(INFO) << PowerStateToString(state_) << " -> "
             << PowerStateToString(state);
   ReadBrightness();
   state_ = state;
   bool changed_brightness = WriteBrightness();
 
   if (light_sensor_)
     light_sensor_->EnableOrDisableSensor(state_);
 
   if (GDK_DISPLAY() == NULL)
@@ skipping 152 matching lines @@
     WritePrefs();
 }
 
 void BacklightController::TurnScreenOff() {
   if (state_ == BACKLIGHT_IDLE_OFF && GDK_DISPLAY() != NULL)
     CHECK(DPMSForceLevel(GDK_DISPLAY(), DPMSModeOff));
 }
 
 
 }  // namespace power_manager