The TLV320ADCx140 parts support Dynamic Range Enhancer (DRE) as defined
in Section 8.3.2 of the data sheets.

The DRE achieves a complete-channel dynamic range as high as 120 dB.
At a system level, the DRE scheme enables far-field, high-fidelity recording
of audio signals in very quiet environments and low-distortion recording in
loud environments.

There are 2 enables for DRE.  The first is a global setting that enables
the DRE engine in the device and the other enable is per channel.  If
the DRE is enabled globally then either DRE or AGC can be used per each
configured channel.  If global DRE is disabled then even setting the DRE
enable bit in the channel config register will have no effect.
Signed-off-by: Dan Murphy <dmurphy@ti.com>
Link: https://lore.kernel.org/r/20200221181358.22526-1-dmurphy@ti.comSigned-off-by: Mark Brown <broonie@kernel.org>