#8526 HIGH 8.2.0 (: display backlight dims for no good reason

[Zarro Boogs per Child]

#8526: display backlight dims for no good reason
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 Reporter:  thomaswamm           |         Owner:  cjb                              
     Type:  defect               |        Status:  new                              
 Priority:  high                 |     Milestone:  8.2.0 (was Update.2)             
Component:  power manager (OHM)  |       Version:  Development build as of this date
 Keywords:                       |   Next_action:  reproduce                        
 Verified:  0                    |     Blockedby:                                   
 Blocking:  8006                 |  
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 This is a fresh restart of #8006 which got too long and confusing.

 Under some conditions, if the display backlight is set to maximum
 brightness, the backlight later unexpectedly dims, and can only be
 restored by using the 'brighten' key on the keyboard.  There are multiple
 variations of this bug, ranging from barely perceptible, to amusing, to
 extremely annoying.  There are easy remedies, but they need to be taught
 or discovered.  It would be better to fix this bug than try to teach
 thousands of users how to avoid it.

 Observed with beta build 8.2-760 (Q2E17 firmware) on a G1G1 XO while
 running Firefox-6 activity and preparing this Trac ticket.  Similar
 observations under more confused circumstances go back a few weeks to
 joyride-2301 (see #8006).

 == Some terminology first ==

 'Brighten' means press the key that brightens the backlight.

 'Dim' means press the key that dims the backlight.

 The backlight is user-settable to 9 different levels using the 'Dim' and
 'Brighten' keys:

  * Level0 (or OFF) is total darkness (backlight OFF).
  * Level1 to Level7 are intermediate brightness levels.
  * Level8 (or MAX) is maximum brightness.
  * LevelT is an arbitrary user-chosen or test level.

 You can get to Level0 (or OFF) by pressing Dim 8 times, or by pressing
 alt-Dim.

 You can get to Level8 (or MAX) by pressing Brighten 8 times, or by
 pressing alt-Brighten.

 'PlugIn' means insert the power adapter plug into the XO, to charge the
 battery.

 'PlugOut' means pull out the power adapter plug from the XO.

 'TimeT' means wait (do not touch XO) for a user-chosen test interval.  Use
 2 minutes as a starting point.

 == How to reproduce the backlight bug - PowerPlug Method ==

  1. Disable both Power Management options in Control Panel.
  1. Dim to OFF (or LevelT).
  1. PlugIn (or PlugOut).
  1. Brighten to MAX.
  1. PlugOut (or PlugIn).  Observe: backlight dims unexpectedly!
  1. Brighten to MAX.
  1. Wait a minute (Do not touch XO).  Observe: backlight dims
 unexpectedly!

 == How to reproduce the backlight bug - Waiting Method ==

  1. Disable both Power Management options in Control Panel.
  1. Dim to OFF (or LevelT).
  1. Wait a couple minutes (count slowly to 100), or TimeT.
  1. Brighten to MAX.
  1. Wait a minute.    Observe: backlight dims unexpectedly!
  1. Brighten to MAX.
  1. PlugOut (or PlugIn).  Observe: backlight dims unexpectedly!

 Sometimes the dimming is synchronous with a keystroke. (More exploring
 needed.)

 '''Remedy''':  The bug seems to occur only if backlight is at MAX, so
 '''to avoid the bug, keep backlight below MAX'''.

 To be explored:  What TimeT is needed to activate the bug?  Knowing this
 might lead to the offending code.

 Can anyone else reproduce this bug?  Please respond with positives and
 negatives.  There might be unknown variables or prerequisites.

-- 
Ticket URL: <http://dev.laptop.org/ticket/8526>
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