On Tue, Aug 19, 2014 at 03:44:23PM +0100, Russell King - ARM Linux wrote:

On Tue, Aug 19, 2014 at 07:15:07PM +0530, Vinod Koul wrote:

quoted

On Thu, Aug 14, 2014 at 09:57:53AM +0100, Russell King - ARM Linux wrote:

quoted

It's got something to do with the async engine API, and seems to be
something to do with whether a descriptor can have other transactions
added to it, and whether a descriptor can be re-used (async-tx engines
typically allocate a fixed set of descriptors and recycle them.)

Yes this is my understanding too. Async API IIUC can reuse descriptors and
if engine doesnt support this is a way to tell them please do use that.

For slave dmanegine API we need to ignore it.

We shouldn't ignore it - ignoring it makes it harder to implement a DMA
engine driver which supports both the slave and async APIs, because
we then need to know the reason for the channel being requested.

Do you have such usage coming up near future :)

Ignoring it until it can be understood and documented is an approach I
would agree with though.

Certainly, I am asking Dan to add more clarity on these bits to help
improve.

-- 
~Vinod