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.
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