Make it an ALSA SOC mixer.
Possible bit rates are:
	100 kbit/s
	400 kbit/s sometimes (depending on supply voltage)
Supposed to monitor V_ref in an elaborate scheme for initialization fini.
I²C:
	input low <= 1 V.
	input high >= 3 V.
	SDA (ACK) pull down voltage = 0.4 V.