Hi Arnd,

On 06/14/2012 06:48 AM, Arnd Bergmann wrote:

[snip]

This would let us handle the following cases very easily:

1. one read-write channel

	dmas = <&dmac 0x3 match>;

2. a choice of two read-write channels:

	dmas = <&dmacA 0x3 matchA>, <&dmacB 0x3 matchB>;

3. one read-channel, one write channel:

	dmas = <&dmac 0x1 match-read>, <&dmac 0x2 match-write>;

4. a choice of two read channels and one write channel:

	dmas = <&dmacA 0x1 match-readA>, <&dmacA 0x2 match-write> 
			<&dmacB match-readB>;

And only the cases where we have more multiple channels that differ
in more aspects would require named properties:

5. two different channels

	dmas = <&dmac 0x3 match-rwdata>, <&dmac 0x1 match-status>;
	dma-names = "rwdata", "status";

6. same as 5, but with a choice of channels:

	dmas = <&dmacA 0x3 match-rwdataA>, <&dmacA 0x1 match-status>;
		<dmacB 0x3 match-rwdataB>;
	dma-names = "rwdata", "status", "rwdata";


With a definition like that, we can implement a very simple device
driver interface for the common cases, and a slightly more complex
one for the more complex cases:

1. chan = of_dma_request_channel(dev->of_node, 0);
2. chan = of_dma_request_channel(dev->of_node, 0);
3. rxchan = of_dma_request_channel(dev->of_node, DMA_MEM_TO_DEV);
   txchan = of_dma_request_channel(dev->of_node, DMA_DEV_TO_MEM);
4. rxchan = of_dma_request_channel(dev->of_node, DMA_MEM_TO_DEV);
   txchan = of_dma_request_channel(dev->of_node, DMA_DEV_TO_MEM);
5. chan = of_dma_request_named_channel(dev->of_node, "rwdata", 0);
   auxchan = of_dma_request_named_channel(dev->of_node, "status", DMA_DEV_TO_MEM);
6. chan = of_dma_request_named_channel(dev->of_node, "rwdata", 0);
   auxchan = of_dma_request_named_channel(dev->of_node, "status", DMA_DEV_TO_MEM);

In the above examples, did you imply that the of_dma_request_channel()
function would return a type of "struct dma_chan" and so be calling
dma_request_channel() underneath?

I am been prototyping something, but wanted to make sure I am completely
aligned on this :-)

Cheers
Jon