#11398 NORM Not Tri: On XO-1.75, flash of random data appears on screen at reboot or power-down

[Zarro Boogs per Child]

#11398: On XO-1.75, flash of random data appears on screen at reboot or power-down
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 Reporter:  wad                    |                 Owner:             
     Type:  defect                 |                Status:  new        
 Priority:  normal                 |             Milestone:  Not Triaged
Component:  kernel                 |               Version:  1.75-B1    
 Keywords:  XO-1.75, reboot, DCON  |           Next_action:  diagnose   
 Verified:  0                      |   Deployment_affected:             
Blockedby:                         |              Blocking:             
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 On an XO-1.75 B1 or C1 laptop, running recent firmware and OS builds (like
 Q4C03 and OS883), a flash of random data frequently appears on the screen
 when rebooting or powering down.

 The random data appears as colored static.  The timing is just as the UL
 warning is being put up -- the static usually changes to become the UL
 warning.  On at least one occasion, the static remained displayed until
 the laptop rebooted.

 My hypothesis is that this is a race condition in the code.   The GPIO
 which tells the DCON to load its frame memory from the video stream is
 asserted, but before it has time to load the memory (it takes at least two
 frame interrupts after GPIO assertion), the DCON is told via the I2C bus
 to switch the display to "DCON master" mode.

 In some cases, the SoC goes so far as to disable the video output before
 the DCON has a chance to grab the video, and the display memory remains
 uninitialized until OFW starts up again.

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Ticket URL: <http://dev.laptop.org/ticket/11398>
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