On Mon, Mar 11, 2019 at 04:43:39PM +0100, Jaroslav Kysela wrote:

> I would not use any of the "user space" ioctl API to represent the
> hardware bclk requirements. The applications should know just the DMA
> memory layout.

> Also, think about the multiple simultaneous paths for the audio output
> in the sound controller (so one DMA from the user space to the
> controller, but the controller can do multiple simultaneous outputs
> using different clocks combining different wire buses or so). Yes, it's
> the corner case, but it's another reason to have the bclk code totally
> separated from the user space ALSA's PCM API.

There's also a range of devices that either don't have visible buses at
all due to integration or which are on buses that look nothing like the
I2S/DSP mode style of bus, rendering the parameters meaningless.