On Wed, Mar 22, 2017 at 09:38:28AM -0600, Stephen Warren wrote:

> Now the BCM2835 I2S controller does appear to have a few features beyond
> plain I2S/DSP modes, that not all I2S controllers might have, such as:

> - Frame length, FS length, channel position, and channel width are specified
> at bit resolution rather than byte/sample/...

> - PDM mode (for digital mics).

> - Sign extension of RX data.

> So, the controller can generate/receive some formats beyond plain I2S/DSP,
> but to be honest I doubt that this level of detail needs to be exposed to
> the ALSA/ASoC core or user-space, nor is it required to interface to any
> typical HW, so it can be hidden in the driver's register programming
> implementation.

At the minute the driver doesn't even support these features, it just
supports plain stereo I2S mode and it *may* be that all that's needed
here is the addition of the DSP modes.