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
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.c
Yes, 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.txt
Yes, 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 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.
Quoted 2 lines
One minor point though is that I'm working on pxa27x. If the serie is not compatible in a way with pxa27x, I won't be able to do anything.
No, it should work just fine on pxa27x.
Quoted 2 lines
Another point I'd like to know, is what is the performance penalty in using dmaengine, and do you have any figures ?
The DMA transfers themselves certainly perform equally well, and the framework is just a thin layer. Where would you expect performance penalty?
Quoted 3 lines
Lastly, they was debug information to debug descriptors chaining, channel statuses, requestors. I didn't see where these had gone, could you point me to the right file ?
Such a debug interface is not part of the mmp-pdma implementation at this point, and the core doesn't have a generic debugfs feature either. If you need that, we'd have to add it back.
FWIW, I attached my work-in-progress patch for this driver which just does some basic dmaengine preparations. Be aware that this does not even compile, it's really just a snapshot.
Thanks,
Daniel
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