[Trac #1412] Switch from driving the panel from the Geode to the DCON when the display is idle.

[Zarro Boogs per Child]

#1412: Switch from driving the panel from the Geode to the DCON when the display
is idle.
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 Reporter:  jg               |        Owner:  rsmith 
     Type:  enhancement      |       Status:  new    
 Priority:  high             |    Milestone:  BTest-4
Component:  x window system  |   Resolution:         
 Keywords:  power            |  
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Comment (by wmb at firmworks.com):

 The turn-on delay occurs because you are supposed to synchronize the GPU
 vertical frame to coincide with the DCON's, to prevent display artifacts.
 You have to wait for a DCON vertical retrace, then turn on the CPU's
 display clock.

 Reference: DCON Specification, page 11, second paragraph.

 Even if the CPU's DOTCLK remains on, the possibility of clock drift must
 be considered, in which case we might have to restart the clock
 synchronously with the DCON frame to avoid display artifacts.
 Experimentation will be necessary to establish what level of complexity is
 required.  Based on my experience with DCON so far, the job is not likely
 to be a "slam dunk".

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Ticket URL: <http://dev.laptop.org/ticket/1412#comment:5>
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