Messages in this thread | | | Date | Fri, 16 Mar 2012 10:36:40 +0100 (CET) | From | Guennadi Liakhovetski <> | Subject | Re: [PATCH/RFC] dmaengine: add a slave parameter to __dma_request_channel() |
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On Mon, 12 Mar 2012, Vinod Koul wrote:
> On Fri, 2012-03-09 at 13:20 +0100, Guennadi Liakhovetski wrote: > > It can be made to work as long as there's only one DMAC group with > > configurable channels and all other DMACs are dedicated to specific > > peripherals, yes. I don't know whether there are already now or are > > approaching any platforms with multiple reconfigurable groups. > And that is what I am talking about. > > Having specific channel mapping given by platform for all channels which > are to be used dedicated. And a pool of channels which can be used by > anyone (if they can be) on a platform. > > Does this proposal sound good for others as well. I think we can target > this for next merge cycle, we are too late for the current one.
Ok, let me try to summarise, what this would mean for sh-mobile:
1. this proposal introduces a new special case: with or without a mapping, that will have to be handled in affected client and DMA controller drivers. E.g., on sh-mobile some devices might on some systems use channels from "general purpose" DMA controllers (no mapping), on other systems it will be a dedicated controller (fixed mapping).
2. this will break, if we get more than 1 "general purpose" type with different supported client sets. So, we develop a new API with a pre-programmed limitation.
3. this will mean a substantial driver and platform code modification. Nothing super-complex, but still some.
4. we'll need a 3-stage channel allocation / configuration: request, filter, config. Whereas with my configuration-parameter proposal it's just one stage: allocate-and-configure.
So, yes, this would be doable, but it doesn't look like a very good solution to me.
Thanks Guennadi --- Guennadi Liakhovetski, Ph.D. Freelance Open-Source Software Developer http://www.open-technology.de/
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