[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.
-----------------------------+----------------------------------------------
 Reporter:  jg               |        Owner:  rsmith
     Type:  enhancement      |       Status:  new   
 Priority:  normal           |    Milestone:  CTest 
Component:  x window system  |   Resolution:        
 Keywords:                   |  
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Old description:

> If the GPU is idle for some length of time, (say, several frame times),
> it will almost certainly make sense to turn off the video drivers to the
> DCON and switch to DCON mode, to reduce the power consumption caused by
> the video drivers and the memory accesses to main memory.
>
> X knows if someone is using the GPU; we have a place to stand for the
> system software to make this decision.
>
> JG's not quite sure the best implementation strategy; we could have a
> dead-man switch in the kernel driver, or set up some sort of idle timer
> in the X server (or probably other implementation strategies as well.
>
> As always, we should measure the benefit to understand the proper idle
> time: the cost here is the latency for the Geode to resume driving the
> display (which is short, but possibly perceptable).  And it may want to
> be policy based as well, depending on whether we are on battery power or
> not.

New description:

 If the GPU is idle for some length of time, (say, several frame times), it
 will almost certainly make sense to turn off the video drivers to the DCON
 and switch to DCON mode, to reduce the power consumption caused by the
 video drivers and the memory accesses to main memory.

 X knows if someone is using the GPU; we have a place to stand for the
 system software to make this decision.

 JG's not quite sure the best implementation strategy; we could have a
 dead-man switch in the kernel driver, or set up some sort of idle timer in
 the X server (or probably other implementation strategies as well).


 As always, we should measure the benefit to understand the proper idle
 time: the cost here is the latency for the Geode to resume driving the
 display (which is short, but possibly perceptable).  And it may want to be
 policy based as well, depending on whether we are on battery power or not.

-- 
Ticket URL: <http://dev.laptop.org/ticket/1412#comment:1>
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