On Mon, Oct 12, 2020 at 07:31:47PM +0300, Andy Shevchenko wrote:
> On Mon, Oct 12, 2020 at 04:48:03PM +0100, Mark Brown wrote:
> > On Mon, Oct 12, 2020 at 04:55:27PM +0300, Andy Shevchenko wrote:

> > > 	if (ret != DMA mode ok)
> > > 		ret = try PIO mode;

> > > which makes OF dependent parts gone along with relying on the properties rather
> > > than real resource availability.

> > I don't understand the blocker to writing that code at the minute?

> Return code in both cases DMA okay, DMA is not okay is 0.

Ah, right - we don't really expose the resulting component to the
drivers.  Although we don't appear to have any drivers doing the open
coding you suggest?  The active use case we have is for drivers
(currently only the STM32 SAI AFAICT) that always do DMA but only do one
direction (not half duplex, a single direction on a given DAI).  They
don't want to fall back to PIO, they want to know which channel is
valid.  It's not just a DMA/no DMA question, it's also which of the DMA
channels are valid.