ARM: pxa: move core and drivers to dmaengine
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Cover letter [PATCH 00/20] ARM: pxa: move core and drivers to dmaengine
Quoted 33 lines · Daniel Mack
Hi Robert,
Quoted 11 lines · Robert Jarzmik
Quoted 5 lines · Daniel Mack
* camera driver:
I started the transition, but I'm not sure how much sense that makes without access to the hardware. I'd much appreciate if anyone could volunteer for this piece; I'll happily share what I got so far. Sascha, Sachin, Guennadi?Hi Daniel,
Do you mean this driver ? :
drivers/media/platform/soc_camera/pxa_camera.cYes, exactly.
Quoted 7 lines
In that case I might help. But before I can do that, I have to be convinced that dmaengine can deal with this driver. I'm thinking in particular of :
- "hot running DMA" queuing
- multiple DMA channel synchronization (ie. 3 channel sync)All that is described in there :
Documentation/video4linux/pxa_camera.txtYes, I've seen that, and while the documentation about all that is excellent, I lack an explanation why things are so complicated for this application, and why a simple cyclic DMA approach does not suffice here. I'm sure there's a reason though.
There might be need to teach the dmaengine core more functionality, but in order to do that, we first need to understand the exact requirements.
Quoted 6 lines
Quoted 3 lines
If someone with dmaengine knowledge could have a look at pxa_camera.txt (maybe Vinod ?) and tell me that
dma_engineframework fullfills the 2 requirements, then I'll be happy to help.Yes, Vinod and and Dan are certainly the best ones to comment on that I think.
I read the file esp the "DMA flow" and "DMA hot chaining timeslice issue". I can say with "properly" implemented dmaengine driver this is very much doable.
Have you guys read: Documentation/dmaengine.txt?
So for "hot chaning" it would work as follows:
Client, allocates and channel and prepares the descriptors A B & C Client (video), submits buffer A, Buffer B. Both are queued by dma driver Client calls dma_async_issue_pending
DMA driver will start Buffer A. It gets the completetion for A and then Starts B. It will invoke callbakc for A.
If you submit C, and invoke dma_async_issue_pending(), C is queued On B completetion, the DMA driver will start C and invoke callback for B.
If B completes before C is submitted, after submit and invoking dma_async_issue_pending(), the C buffer will be queued and started.
~Vinod