[PATCH] of: Add generic device tree DMA helpers

[Arnd Bergmann]

On Monday 19 March 2012, Mark Brown wrote:
> On Sat, Mar 17, 2012 at 10:47:51AM +0000, Grant Likely wrote:
> 
> > After implementing both schemes (ie. interrupts+interrupt-names && [*-]gpios)
> > I definitely prefer the fixed property name plus a separate names property.
> > It is easier to use common code with that scheme, and easier to statically
> > check for correctness.
> 
> It's not a fantastic experience when using the bindings as the arrays
> grow large, though - keeping things matched up isn't much fun especially
> if any of the elements in the array are optional.

Maybe one can use named properties in a new device node in that case,
like this:

	bus {
		dma: dma-controller {
			#dma-cells = <1>;
		};

		device {
			compatible = "device";
			channel: dma-channel {
				type = <0x1>;
				name = "foo";
				number = <23>;
				direction = <3>;
			};
			dma-requests = <&dma &channel>;
		};
	};

In this case, the dma engine's filter function would look up
the dma-channel device node from the phandle passed in the argument
to the dma-requests property, while a simpler dma engine would
just use a single number to identify a channel there.

	Arnd