#11644 LOW 1.75-so: Camera LED may flash briefly during resume

Zarro Boogs per Child bugtracker at laptop.org
Fri Feb 24 14:49:38 EST 2012

#11644: Camera LED may flash briefly during resume
           Reporter:  greenfeld  |       Owner:  corbet                           
               Type:  defect     |      Status:  new                              
           Priority:  low        |   Milestone:  1.75-software                    
          Component:  kernel     |     Version:  Development build as of this date
         Resolution:             |    Keywords:                                   
        Next_action:  diagnose   |    Verified:  0                                
Deployment_affected:             |   Blockedby:                                   
           Blocking:             |  

Comment(by corbet):

 I've finally had a chance to look at this.  In short: the brief power-up-
 on-resume behavior is deliberate.

 What it comes down to is that the driver doesn't really know what could
 happen at resume time; in particular, an interrupt might be delivered.  As
 it happens, any attempt to access the camera controller registers while
 the controller is powered down leads to consequences rather less pleasing
 than a briefly flashing LED.  The system simply stops dead in its tracks.
 After fighting this kind of trouble for a bit, I concluded it was better
 just to bring the controller up briefly.

 Of course, powering up the controller does not turn on the LED; it's
 sensor power that does that.  There is no real reason why the sensor needs
 to be powered on unconditionally at resume time.  So I guess I'm saying,
 in my long-winded way, that this is fixable, though I'll need to test the
 result well.  Stay tuned.

Ticket URL: <http://dev.laptop.org/ticket/11644#comment:4>
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