#10127 BLOC 1.5-sof: DMA image corruption from camera in C3/C4

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#10127: DMA image corruption from camera in C3/C4
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 Reporter:  cjb      |                 Owner:  corbet             
     Type:  defect   |                Status:  new                
 Priority:  blocker  |             Milestone:  1.5-software-update
Component:  kernel   |               Version:  not specified      
 Keywords:           |           Next_action:  diagnose           
 Verified:  0        |   Deployment_affected:                     
Blockedby:           |              Blocking:                     
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 We're seeing corrupted camera data when the CPU drops into C3 or C4.
 Booting with "processor.max_cstate=2" eliminates these effects.

 This bug tracks finding a way to avoid the corruption.  Jon C's already
 asked Via about it, without any progress.  There's a patch that attempts
 to fix clocking when we're in C3/C4 committed to git here:

 http://dev.laptop.org/git/olpc-2.6/commit/?h=olpc-2.6.31&id=7e78e4fa3c693179facaf0467d148b57c40f90e6

 .. but it doesn't seem to be working; the corruption still occurs.

 An obvious(ly ugly and hacky) workaround would be to refuse to enter C3/C4
 whenever the camera's streaming.  Jon N wonders whether it might be the
 case that we're simply not supposed to DMA in those states, because of
 unvalidated CPU caching.

 Jon C, any ideas?  Thanks.

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Ticket URL: <http://dev.laptop.org/ticket/10127>
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