Messages in this thread | | | Subject | Re: [PATCH/RFC] dmaengine: add a slave parameter to __dma_request_channel() | From | Vinod Koul <> | Date | Mon, 19 Mar 2012 17:09:04 +0530 |
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On Fri, 2012-03-16 at 11:16 +0100, Linus Walleij wrote: > On Fri, Mar 16, 2012 at 10:36 AM, Guennadi Liakhovetski > <g.liakhovetski@gmx.de> wrote: > > > 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. > > I fail to see why this would not be solved by a one-to-many mapping? > > Flag for each device which channels it may use in a mapping > table in platform data or device tree, I don't see the problem. > > You don't even have to specify that on a per-channel basis if > you can come up with something more clever in the mapping > table, such as "this device can use any channel on this DMAC, > and channels 1-7 on that DMAC" - no problem? Thats why added channel number to your proposal :) > > > 3. this will mean a substantial driver and platform code modification. > > Nothing super-complex, but still some. > > Big deal. Refactoring is fun... ;-) > > > 4. we'll need a 3-stage channel allocation / configuration: request, > > filter, config. > > In my world: channel request with *NO* filter function. > > Filter functions are part of the problem. So we refactor these > away as part of this change. That's the whole point... > > The core gathers information from the platform and the > DMAC driver(s) to build up the constraints necessary to > hand out workling channels to each device that request > one. > > And Russell IIRC already suggested a request-and-config > channel inline for the simple cases, and if you still need to > explicitly runtime-reconfigure then that's for a good > reason. > > > Whereas with my configuration-parameter proposal it's just > > one stage: allocate-and-configure. > > For one specific hardware, yes. For DMAengine at large > and the majority of the drivers, no. right, and that is my main concern. > > Yours, > Linus Walleij > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/
-- ~Vinod
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