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

[Zarro Boogs per Child]

#10127: DMA image corruption from camera in C3/C4
--------------------------------+-------------------------------------------
           Reporter:  cjb       |       Owner:  corbet             
               Type:  defect    |      Status:  new                
           Priority:  blocker   |   Milestone:  1.5-software-update
          Component:  kernel    |     Version:  not specified      
         Resolution:            |    Keywords:                     
        Next_action:  diagnose  |    Verified:  0                  
Deployment_affected:            |   Blockedby:                     
           Blocking:            |  
--------------------------------+-------------------------------------------

Comment(by corbet):

 OK, I've pushed a patch to my olpc-2.6.31-cam tree; it uses pm_qos to keep
 the CPU from going below C2 while the camera is streaming.

 It works.  Interestingly, though, I have to disable C3 entirely while
 streaming - not just while DMA is active.  That suggests that the real
 problem is not necessarily in the DMA engine - it might be the video
 capture engine.  Perhaps I never noticed it prior to enabling DMA because
 the CPU never went idle when it had to copy frames to user space itself.

 Anyway, sorry this took this long; I should have put in a patch like this
 some time ago.

-- 
Ticket URL: <http://dev.laptop.org/ticket/10127#comment:3>
One Laptop Per Child <http://laptop.org/>
OLPC bug tracking system