On Monday 10 March 2014 07:27:48 David Woodhouse wrote:

quoted

There are multiple reasons why
we have to pass the dmaengine device to the dma-mapping API at the moment
rather than the slave device, but in essence it comes down to the engine
being the one that is the master on its parent bus. A trivial example
where it goes wrong would be the slave living on a 32-bit noncoherent bus
and the master living on a 64-bit coherent bus.

That's true in the general case, certainly. But in this case we're
basically just talking about different functions of a multifunction
device. 

Ah, I thought you were talking about a generic SoC with lots of units
on it.

It may turn out that we need the *flexibility* to specify which
device shall be used for DMA mappings for a given channel, even if in
*most* cases it ends up being the DMA controller itself.

Yes, that would probably work with a helper function that can
pull the right device structure out of the ACPI description (or
whatever the DMA engine needs) given the dma channel pointer, or
fall back to the dma engine.

	Arnd