I'm investigating a problem with the SGTL5000 on our custom board. We are using Pulseaudio and find that if the LINE-IN of the SGTL5000 is not connected to an external earth, it will automatically enable its digital mute *on the LINE-OUT*. It is totally unclear how this happens as I am monitoring the I2C bus transactions and the last time the digital mute is unset we find it is immediately read back as correctly unset. (Digital mute == DAC_MUTE_LEFT and DAC_MUTE_RIGHT)
When we find the digital mute to be self-setting, we also see the VOL_BUSY_DAC_LEFT/VOL_BUSY_DAC_RIGHT bits to be staying high and never going low.
Has anyone else come across this or can suggest why these bits are automatically being set? It doesn't make a lot of sense that the audio input must be grounded for the audio output not to be self-muted.