The Mixer couples analog input from 4 sources (DAC, Line In, Mic 1,
 Mic 2) each input has its own gain & mute controls.

At the moment only DAC is implemented fully and Line In path can be
switched on/off. The patch implements Mic 1 and Mic 2 paths and fully
implements Line In path.

Manual states that these controls (16.6.3.3 Programmable attenuation:
GOi) gain varies from -22.5dB to +6.0dB with 1.5dB step. Also there's
extra values below the minimum, but they behave the same as the minimum
value.
Signed-off-by: Siarhei Volkau <lis8215@gmail.com>
Link: https://lore.kernel.org/r/20221016132648.3011729-7-lis8215@gmail.comSigned-off-by: Mark Brown <broonie@kernel.org>