On Monday 07 May 2012, Stephen Warren wrote:

quoted

That way dmac and client drivers using DT could do away with the filter_fn.

Roughly speaking (I am not very well versed with DT syntax)

Client Node:-

mmc1: mmc at 13002000 {
        ...
        dma_tx = <891>   //some platform-wide unique value
        dma_rx = <927>   //some platform-wide unique value
        ...
 };

I believe we specifically don't want to introduce any global concept of
DMA channel ID, either within the kernel, or at the device tree level.

I agree.

While we do have global interrupt and GPIO IDs within the kernel, this
has caused problems, I think primarily due to the need to manage this
unified namespace and allocate a single global ID for a bunch of
different ranges of controller-specific IDs.

Within device tree, everything is always represented as an ID
relative-to or within a particular controller, so it's easy to namespace
things separately.

Right. Note that strictly speaking the requirement is that everything
is local to a particular namespace, which does not have to be the
device controlling the property.

For instance, we can map interrupt numbers to different controllers
using the interrupt-maps property. It is a fairly complex method,
but something similar or a somewhat simpler method could be applied
to define a namespace for dma controllers from which you can pick
a request line.

The example I've given earlier does just that.

	Arnd