[PATCH 00/20] ARM: pxa: move core and drivers to dmaengine
zonque at gmail.com
Sat Aug 10 06:56:19 EDT 2013
On 10.08.2013 00:50, Robert Jarzmik wrote:
> Daniel Mack <zonque at gmail.com> writes:
>> * 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 ? :
> 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 :
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.
> If someone with dmaengine knowledge could have a look at pxa_camera.txt (maybe
> Vinod ?) and tell me that dma_engine framework 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
> 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.
> 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?
> 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.
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