Re: [PATCH 1/4] dt-bindings: Document the STM32 DMA bindings

[Arnd Bergmann <arnd-r2nGTMty4D4@public.gmane.org>]

On Thursday 08 October 2015 18:01:23 M'boumba Cedric Madianga wrote:
> Hi Arnd,
> 
> 2015-10-08 17:43 GMT+02:00 Arnd Bergmann <arnd-r2nGTMty4D4@public.gmane.org>:
> > On Thursday 08 October 2015 17:20:09 M'boumba Cedric Madianga wrote:
> >> +Each dmas request consists of 5 cells:
> >> +1. A phandle pointing to the STM32 DMA controller
> >> +2. The channel id
> >> +3. The request line number
> >> +4. A 32bit mask specifying the DMA channel configuration
> >>
> >
> > It's fairly unusual to encode the channel id here, rather than
> > letting the driver pick one. Is that actually required here?
>
> Yes it is required as in STM32 platform the channel/request DMA
> mapping is done by hardware lines.
> So, if one client wants to use DMA, he has to choose the correct
> channel/request values according to the DMA mapping of his STM32
> platform.
 
Interesting. So you have seven channels ans seven request lines,
with a random but fixed mapping between them?

How do you know which channels are available for memory-to-memory
transfers?

	Arnd
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