I want to disable the mic input and therefore called the SGTL5000 micGain with parameter 0. When doing this I noticed that my Line-In level also dropped.
I looked into the code(file "control_sgtl5000.cpp") and found
return write(CHIP_MIC_CTRL, 0x0170 | preamp_gain) && write(CHIP_ANA_ADC_CTRL, (input_gain << 4) | input_gain);
in function micGain(line 622).
For me it looks like that not only the microphone gain is set (CHIP_MIC_CTRL) but also the input level (CHIP_ANA_ADC_CTRL).
Is that intended? (the function name implies that only mic gain is effected...)