On Thu, Sep 18, 2014 at 08:08:52PM +0300, Andy Shevchenko wrote:
> In case of DMA we never got things done until we enable both channels. In case
> of receive only or send only mode the user has to provide a dummy buffer.

The driver must never impose such requirements on clients, they
shouldn't need to know about the quirks of the controller.  There's
support in the core providing dummy buffers for transmit and receive,
you should use that (possibly extending it so the dummies are only
provided for DMA).